17. Join that sports league that you've always dreamed about joining when you "get more time" (no time like the present!).
Whether it's a softball league, an ultimate Frisbee league, or a soccer league, there are plenty of intramural-style sports leagues open for registration in the summer. You're never going to have enough time to play in one (at least, you don't think you do) but we get the feeling that once you play a game or two, you'll make time for it. It's fun, relatively cheap, and a great way to meet new people.