[Meta] The answers will be way more informative if they are posted as "X instead of doing/learning Y" e.g. "Underwater basket weaving instead of moping around" as of course I wished I had learned everything.

(Similar to Fluttershy) Culturally, there's a belief that college years are our formative years, and we should be learning to be good, well-rounded (in the liberal arts sense) people. But college is a huge time and money commitment, and the job market is competitive, so I think college ought to be used strategically for advancement in academic or well-paved professional tracks (doctor, lawyer). My college, Harvey Mudd, had a noticeable emphasis on ethics in science and technology and humanities as a hearty side heaping to technical topics. Ideally, ethics would be strategic for career advancement, but in the real world (software engineering), it's never seem to come up in my job placement. Harvey Mudd should be a pretty good model though since they manage to make it work anyway. Alan Kay also suggested a technical and humanities double major (somewhere in that interview...).

The politics of college aside, here's my list of things to learn as soon as and by any means possible:

• Rationality. Goes without saying here. In particular: using reasoning and empirical data for important questions. I just came across this today that decries the complete lack of empirical basis for programming language design (a topic that's collectively consumed hundreds of thousands of hours of debate, not to mention time developing mediocre solutions). You'll see the same thing in any field (at least fields that are mature enough to even ask the question).
• Career & finance. Understanding that there's a game to both and having knowledge about those games can get you opportunities and money that you wouldn't otherwise. I recommend Ramit Sethi's material and Tony Robbin's new book.
• Body & brain. You can often get away with research + rationality for a particular question, but it's good to have prior exposure to solutions to common problems: nutrition/fitness, body language, learning, mental health. For example: thinking "I'm depressed" leads you to: it could be due to a nutritional or neurochemical imbalance, or fixed with changing some thinking habits; instead of "I'm depressed because I'm a failure at life."
• Technical topics. If you want to make a contribution you really need to focus. Math is generally useful, but that's mostly as a symbolic and visual language rather than any particular deep math topic until you need it. Programming is often useful for automating technical tasks. I've observed people who study physics excelling in different topics. (Perhaps exposure to model building and data-driving theory testing. Perhaps selection bias.)
• Philosophical and spiritual things. I've only started to respect this recently, but I've found value in Taoist, Buddhist, Catholic, and Stoic teachings. Here's someone else exploring a variety of areas.
• Microeconomics and game theory come up a lot in the world and knowledge thereof may prevent you from making dumb "If I were in charge..." statements.

Lots of things I wish I knew more about still, like sociology/anthropology, politics, and history, where there's a lot of "why should I learn about this particular thing or another?" that are hard to answer on my own.

Intuition pump: you're going to lose all adult memories tomorrow. You have a budget of ~4 years worth of experiences and skills which you are allowed to keep. What do you elect to retain?

(This question will probably not work so well if you're 22 or under)

I think that learning some basic programming is a skill that can be useful in a variety of occupations. My brother works in procurement, but he has programmed some basic macros that have allowed him to complete his tasks much more efficiently and this helped him gain a promotion.

One of the best courses I ever took was art history. Art is everywhere, in restaurants, in hotel lobbies and scattered around the city. Having an opportunity to discuss various works within a classroom setting was very valuable for improving my ability to analyse art, which furthers my appreciation and allows me to start interesting conversations. I want to try to also take a class in film studies to see if it deepens my appreciation of film.

Statistics are extremely useful and are used everywhere. From the sciences, to business and to sport (see moneyball) it is worth having at least an introduction so that you can at least attempt to understand the evidence behind a theory. Many subjects like business, psychology or the life sciences will force you to take a statistics course anyway.

First year psychology is one of the most interesting and useful courses I've covered too. Psychology covers everything from improving your memory, maintaining motivation, convincing people and understanding happiness.

I haven't taken a course on micro-economics, but I've read articles online. I agree with Joel Spotsky - (http://www.joelonsoftware.com/articles/CollegeAdvice.html), that economics is heavily frontloaded with useful ideas that allow you to understand not only how the business world works, but how to make better decisions in general (arbitrage, Pareto-optimality, time-discounting, specialisation, supply and demand).

Philosophy is valuable because it teaches you to question everything, even your most basic assumptions. Again, this is worth taking in college because of the discussions that you'll (hopefully) have in class. My uni has a course on practical philosophy that I'm planning to do next year.

Don't forget about extra curricula's. You can try to become an exec on a club to gain leadership experience. You can try to find a new hobby. I'll note debating as a particularly interesting activity. Debating calls on knowledge from all different areas - from international relations, economics, law, psychology and philosophy. It improves your ability to think on the fly and to articulate your thoughts. Further, there is a tight feedback loop, adjudicators are usually willing to provide feedback.

I took a Philosophy course that emphasized Aristotle, Sartre, Plato, Freud, Karl Popper, and a handful of psychologists and other philosophers that I frankly didn't bother to remember ten minutes after the final.

It didn't tell me why I'd actually care about philosophy.

Other harder sciences sometimes had this issue -- most notoriously math -- but the answer to a math problem is the same no matter why you're interested in it. That's not really the case here, and that my instructors didn't even feel such an argument was worth mentioning is... frustrating.

Critical skills for getting the most from your career:

Networking - as a general skill, my absolute number 1

Communications - Both written and verbal skills are a must; visual design if you do a lot of visual presentations

Grammar - maybe not too much; your boss probably thinks it's okay to use a comma in front of a subordinating conjunction too

Organizational strategies - I'm not sure if this can be taught. It may be purely a personality trait.

information technology - I doubt this is a problem for most of you; note I do not at all mean computer science which has a much lower value

how to not be a dick

How to evaluate ideas scientifically - Determinism, Parsimony, Probability Estimation, the Scientific Method, Research Methods and their relative validity

Advanced Statistics - this is critical if you're going into academia; the rest of us only really need it to look good on a grad school application and to get by for those couple of years; most advanced mathematics simply never come up in the real world

finance - some important ones are index fund, expense ratio, and IRA

tailoring - this is critical if you're going into law, finance, or politics; not how to tailor but how to evaluate a piece of clothing's quality and to get the right fit; it is also useful for other fields but less so (no, khakis are not typically business appropriate)

Where to look for the best information in your field

as many hundreds of hours of practice as possible in your chosen craft - if your field is performance-driven then this should be done even if it is to the detriment of the other skills I named; if your field is signalling-driven then this should come after the rest of this list

This leaves out all the critical life skills of course.

I wish I knew what I wanted to have studied when I went to college, so that I could have hit the ground running, with a goal in mind. Instead I took a year and half before I had settled on a major of physics. It seems that some people had a better idea of what to get out of college, but that seems largely dependent on their parents, where they grew up, and what part of the internet they lived in. I don't feel like I had a good understanding of what different jobs and careers were like.

So for classes, I took more chemistry than I would have liked, but that doesn't bother me that much, as it was interesting and still relevant to some of my physics classes.

What does bother me, is that I spent a lot of time taking classes that I thought I should take, instead of classes I wanted to take. I thought that doing theoretical physics was a bad idea because of job / grad school prospects (probability of getting a professorship is low) so I took lab classes and did laboratory research that I didn't like as much, and did worse in, than theory classes. I still ended up doing theory in my spare time, and instead of research / laboratory work, but it was at the expense of that work, rather than purely additive. I was thinking that following my 'passion' was a bad idea, but I think that if i did so and did theory it could have worked out better - I would have been happier, and had a better resume in the end.

I have a lot of strong opinions about the physics curriculum, and wish that it had more programming, and less redundancy. I'm not familiar with how physicists get good at modeling or data-science, and can't think of any undergraduates from my school who got much experience with this. But that seems like it would have been a good thing.

Something cool to have learned would be "practical mindsets and values". For a long time I had an idea of that as long as I was learning things, that was great and all I needed to care about. This served me well, but eventually I was introduced to the idea of "get shit done" which was also very useful.

One of the things that everyone learns in university (but usually does not notice to have learned it as it is never listed in any syllabus) is a set of skills and procedural knowledge that is specific to university setting, e.g. how to deal with problems using university resources, how to use them, how to submit forms that are university specific, how to deal with a university administration, how to submit your homework, how to deal with deadlines and so on. Naturally, this procedural knowledge is somewhat less useful (although not useless) outside the university. At the same time, the way "the outside world" works is not diametrically opposite to the way the university works (although it is different), therefore maybe there is a room for some small changes that would be helpful for students that leave academia after they graduate? Suppose a university decides that it would be useful for their students to obtain more procedural knowledge that would be useful in the private (or public) sector. How could they achieve this goal without compromising the things that are good about university life? One obvious answer is to outsource this problem by encouraging students to find internships, but maybe there are more ways to do it?

I wish I had taken more statistics courses. I learned the basics and have picked up a fair amount of the advanced stuff through self-study during graduate school, but I didn't realize during college how useful it would be.

I wish more people would take more computer science courses. Intro to Comp Sci is usually too basic to be useful. Data structures, algorithms, numerical/scientific computing are all useful in a large variety of careers.

I think some sort of debating or arguing class would be very helpful. People should have good reasons for why they do things and this applies to most topics.

Some sort of thing where the topics debated would be marked by how well you cited facts or how clear your chains of reasoning were. So if you were asked to discuss why on food was better than another you should have some process like looking up the answer in a text book or looking up stuff from science websites online, interpreting them correctly, and presenting the truth. Lots of fanfare and marks should be awarded for doing this process successfully so people are trained to see this process as valuable. Lots of effort should be made to make sure people look for good advice sources.

On novel questions, reliable processes like asking a bunch of people their opinions, doing some tests, and presenting those results should be suggested.

For specific knowledge fields clear aid should be provided for these topics- finances. Maths should deal with this a lot. Physical health. Biology should deal with this a lot, in a more comprehensive manner than it does now- I've often seen them address illnesses, but rarely seen science curriculems address good health practices. Sexual health and relationship good practice should be addressed a lot more widely. Those are issues everyone is likely to face and everyone should have a solid foundation of knowledge to aid them with rather than a slapsash compilation of things from random people and the internet.

I am a firm believer in liberal arts and classical education and I would like to see more of that in university and have other things farmed out to technical schools and trade schools. I think of 4 years the first two should be limited to philosophy, language, learning how to think, writing, research, journalism, and then the last 2 years specializing in a field of study within which to excel.

Engineering instead of biology.

I guess there is a spilt between sciences (subjects where you do problem sets) and humanities (subjects where you write essays). All my university education was problem-set based, and now I'm a bit jealous of how good the people who did humanities are at writing. On the other hand, I'm not sure what I would like to sacrifice from my actual education, most of it seems pretty worthwhile too.

I wish I had actually applied myself in studying a foreign language instead of putting in the minimum effort to pass. I wish I had studied computer science, it would had accelerated my career by 5 years and CoSci is fun. I wish other people had taken more English classes, because writing clearly is hard and needs to be taught*.

*My alma mater my be unusual in actually teaching clear writing in English classes. I credit the professors involved.