Plenty of party clothes. Both the kind that you wouldn't want to get messed up and the kind that it wouldn't matter. Being in SoCal, as an 18-year-old freshman, your likely to find yourself in TJ piss ass drunk one night. You should have an outfit for that situation.
Formal and Semi Formal dress. Even if it's not for a sorority formal. At UCSD each college has a formal. That's five opportunities to get all pretty without even going greek.
Duct tape and WD40!!! Universal truth. If you have these, you can fix just about anything!
Ear plugs. For studying or the snoring roommate.
Sunscreen
...Can't think of anymore right now. I'll post as I think of them.