at test center #1, we kept everything under our seats...people would take out their water bottles during the test. we could take our food out during the break and eat to our hearts content.
at test center #2, at the university, we had over 1000 people testing in four lecture halls...there was barely room for us, let alone our *&^%, so we piled our stuff on the floor up front. this meant nothing to drink or eat during the test...it was bad enough to hear 450 people breathing, moaning, scratching, etc. during the test. We actually got goodie bags from Kaplan on the way in, and I brought my own food, so we all were able to eat during the break...that is, if you made it back from the bathroom on time.
Anyways, I'd say pack a large snack and bring something to drink and go with the flow of things. You will have time to eat and drink somewhere along the way. And, oh yeah, it a large breakfast and don't drink too much ahead of time.