First, you should take the minimum number of classes necessary for graduation because school is so much less efficient than other learning methods. (For example, you can watch videolectures from the best professors in the world for free at your convenience. Then download the lectures + VLC, change the playback speed, and learn everything 50% faster.)

As long as you are taking classes, you might as well try to learn things that are a good fit for them.

• Public speaking and acting are good fits for classroom learning.
• Chemistry classes and some others give you a chance to use materials that would be hard to find on your own.
• IMO classes involving computers are an awful fit for classroom learning--it's always easier for me to figure out stuff myself. This includes programming. Only take these if you're going for a compsci degree (but, it is a pretty good degree to have as far as I can tell).
• Take classes by professors that are well-reviewed (see ratemyprofessors.com), especially those with a reputation for high levels of class participation or interesting personalities.
• Also, it's worth choosing classes based on the classmates you expect to have. So consider taking classes full of smart people like physics and game theory.

As for subject matter, I think I became smarter learning physics and economics basics because I became more comfortable applying math and thinking about things in simple, non-intuitive ways. Economics is particularly great for rationality--microeconomics is essentially an extended description of what the world would be like if we were all rational. It's great to have a cheat sheet. Programming was definitely my biggest ever mindfuck, but as I mentioned it's best learned outside school.