Holy crap! Guys, I'm all for self defense but the OP said he was refering primarily to a college campus. Some of the suggestions; baseball bat, machette, tire iron...come again???
School campuses are often very against weapons of any type. I think it would be unusual to find a school that would allow knives, OC spray, ASP's, etc., much less a machette.
And in some states (like the oddball one I live in), carrying a concealed knife is a felony. Carrying a concealed handgun is only a misdemeanor.
If I went to a college where I felt the need to arm myself with a machette while sitting in class I think I'd try to find a new college. Some of these responses I'm hoping are strictly jokes. For a serious answer to the OP, if the school allows OC spray I'd recommend that over a knife, ASP, or anything else besides a gun (I can't immagine any school that allows tasers, or that would be my choice above OC).
I've used all of these (minus the gun/ knife) on people in real life (non training): Winchester baton, ASP, OC, taser. Taser is the most effective, followed by OC (I'm on my 6 or 7th can
). But really, as a student I think discretion would be the better part of valor. Best defense? Common sense and some good running shoes.