When I have to do a lot of hardcore studying I get more hungry...I like to keep something healthy close by, green peppers, apples, carrots...sometimes I also go for chips and popcorn...so long as you don't eat a HEAVY meal that will put you to sleep...I would rather eat 3 little snacks than one huge meal during studying days...I also drink tea and coffee but not to the point where it gets irritated and nervous...only to keep me awake...
And actually, believe it or not, one of the best ways to get going on studying after dozing off is taking a short refreshing break with your notes...sometimes I walk around the library with two or three pages then go back inside for some more hard studying...I know some friends who actually have to work out the days before their exams because it reduces the stress, helps them think faster and sleep less!!!!!