Killing my new-found free time?

As of this week, I am officially done with school. Forever. And aside from a summer job that ends at 1:oo in the afternoon and a web-based internship, my summer is completely open. I'm used to managing a college newspaper so the concept of "free time" to me is foreign and a bit frightening. Aside from hanging out with friends, what are some good non-expensive things to do? I've been playing a metric ton of Street Fighter and catching up on reading, but some of you have cheap and fun hobbies, so I want to hear 'em and know how to get in on them.

Whenever I have too much free time, I usually find myself trying to "fix" things that frankly don't need fixing. However it's one of those "hobbies" that is usually free, but can get real expensive, real quick.  :P

Just walking around or running, that's cheap and fun.

Well, I clicked on this topic because I was sure You need some gaming suggestions (To which I would have answered Just Cause 2). But now I'm a little bit stumped, but won't back out either ;). The problem is how should we suggest You a hobby if we don't know you. Gaming is actually not too expensivo if you just buy all your games a couple of months after release like me (especially on steam they are often 10$ by this time). The only thing I do which is inexpensive is sports, preferably streetball. But I would recommend starting to read up on the topic you wanna study in university (if you wanna study in university). Apart from that maybe build some awesome things, like this here:   http://www.instructables.com/id/MintyBoost!---Small-battery-powered-USB-charger/ 
Or well, learn to play the effin guitar ;).