I'm going to focus more on entertainment in terms of real products as I expect this category to be underrepresented in this thread:

Spotify Premium: ~$10/mo, unlimited commercial-free music streaming (+ ability to sync to mobile for offline listening). They have an enormous library. I have essentially stopped buying albums because they are all available on Spotify (might not be as useful if you listen to really obscure music, but it's worth searching their library before buying a subscription. You may be surprised what they have. I just bought my dad (a huge audiophile and musician) a 6 month subscription for his 65th birthday and he just downloaded Rolling Stone's top 10 albums of the year that he otherwise would have bought and is really happy with it.

Netflix: Unlimited streaming is ~$7/mo, which is all I have. They have a large library and are starting to become content producers as well as just aggregators. Of course if you're easily seduced into binge-watching when you really want to be doing other things, it might not be a good idea. Personally, I get a lot of enjoyment out of it and it's cheaper than one movie ticket a month. Lots of classic movies as well as more modern stuff. However, it's relatively easy to "run out" of stuff to watch on Netflix, at which time you can just cancel your subscription.

Roku: If you don't have a Smart TV, it's the best of all of the 3rd party options (FireTV, AppleTV, Chromecast, etc.). Get the "Roku 3", it's under $100 and has access to a lot of streaming services. The best feature is "Universal Search" where you search for a title and it looks across all of the different streaming services and lets you find the cheapest (or free) offerings. (Not offered as far as I know with any of the other products because they all push their own content stores first).

Aux-port/Cigarette-lighter Car Bluetooth Adaptor: ~$30-$40. Gives you in-car bluetooth if you don't already have it. I recommend the Belkin one on Amazon. It's been well worth the price in terms of added convenience for me.

Windshield/Dash Suction-Cup Mount for Smartphone: Cheap. If you use your phone for driving directions, it's much more convenient (and a lot safer) than having the phone in your lap. Keep in mind that in some areas, it may be illegal to mount it to the windshield.

Radar Detector: ~$200 – $700. Get either a Valentine or a Cobra. They're about the cost of one speeding ticket and can help you avoid tickets. (This is not an endorsement of driving too fast of course). Valentine is simple but effective and indicates front or back direction of radar source. Expensive, but no bells and whistles. Cobra has a wide range of products with a wide range of prices. Not directional, but has lots of bells and whistles like learning false positives, traffic-cam alerts through GPS, and connection to a network for crowd-sourced data (think Waze, but for stuff like speed traps). Again, these may be illegal in your area—make sure to check first.

Tablet/e-reader: I prefer to read textbooks on a tablet and other books on my Kindle Paper-white. Had an iPad provided by my previous employer before I left and I'm really missing it more than I thought I would for textbooks. I'm looking into a new tablet and really want one with good palm-rejection and a stylus for taking notes (If anyone has suggestions, please let me know).

Textbooks: I give myself a monthly education budget and buy a new textbook (and sometimes solutions guide) every couple months. There are also free options of dubious legality like libgen.org or libgen.info. e-textbooks go great with tablets.

Wake-up light / Dawn Simulator Alarm Clock: ~$100 Some love em, some (like Eliezer) don't get any benefit from them. I kept a sleep journal for a month and it seems to work for me. I'm in a much lighter sleep when the alarm finally goes off (if I don't wake up naturally from the light). If you're techy, you can build your own with an arduino or raspberry pi pretty easily. On that note...

Arduino / Raspberry Pi: ~$30-$40. Very fun if you want to learn DIY electronics. Arduino is a microcontroller whereas raspberry pi is a full computer. I'm just getting started learning embedded systems and electronics myself (taking a class on edX starting this month called "Embedded Systems". If anyone else here on LW is planning on taking this, let me know).

My favorite fiction Novel (aside from HPMOR): The Shadow of the Wind - by Carlos Ruiz Zafon. Great story, deep characters, a love story, a mystery, and some of the most beautiful prose I've ever seen.

Nice sunglasses: $15 - $300. Get some brown/amber-tinted, polarized lenses with a nice lightweight aviator frame. You'll never look back. May be a bit hard to find at the lower price point, but not impossible.

Hope some of this was helpful!