Snag extra food and stash it in your room for those "weird" hours when you are so freakin hungry you can't stand it and the buffet is still two hours away. Creme brulee or chocolate pie is a nice option at 3:00 am.
Bring a camera! If you have a digital, bring blank CDs and make friends with someone who brought a laptop so you can snap millions of pix and pop over to their cabin once in a while to dump them and burn a CD. - Thanks Erick!!!
Bring musical instruments if you have them. One of my favorite moments was when I busted out my melodica when a couple of our shipmates broke out their guitars and we had a little jam on the promenade deck - starboard side!
Make friends with a bar tender in an obscure location, ie, not by the main stage. If you're lucky they'll give you double shots for the price if singles!
Bring another band. There's only one band that would not be tiring 8 nights in a row and that's Phish.
Print this entire thread for reference!
Hope this helped!