My biggest regret from college is not getting more involved with the activities/groups my college offered. I was plenty active around campus socially, but I was only in one group my entire four years. (Well, two if you consider being a computer assistant a group.) You will gain a lot and not feel as if you missed out on what your college has to offer by participating -- not to mention all the friendships you'll build in the process. Get out there and join groups!