We always make a run to Uwajimaya before Con. Our staples are:
POCKY!
Ramune
Pork Buns
Wasabi Nuts/Rice Crackers
Some rice balls are easy and cheap to make ahead of time (just so long as you get the sushi rice; it doesn't work with longer grains), and you can stuff them with all sorts of yummies. We also bring Odwalla bars (small, quick, easy, and satisfying), honey roasted mixed nuts (protein lasts longer!), apple slices with crunchy peanut butter, and PBJs. Anyone know of a good sushi place nearby (not good for sitting in a bag all day
)?
Just be sure to strive for somewhat rounded nutrition.. otherwise you'll feel terrible and won't be able to effectively pull those all-nighters
Good luck!