Mostly, if you're under 18, there isn't much to do besides Karaoke, Anime rooms, and the Dances after 10pm. But Stuff starts up the next day bright and early (aka, like, 7-8am).
As good advice, make sure you SLEEP over the weekend, even if its a catnap for 30 minutes at 4am. I didn't sleep my first year, and Sunday ended up as Hell on Crack for me. You get grumpy and your brain stops working, and that just makes it no fun for you or anyone around you.