This is by no means a long term solution, but if you're exhausted from an all nighter and confronted by an early morning lecture, just bring along some menthol cough drops to suck on. It isn't food so no professor will be snootily snubbing you like he would if you were armed with an extra-extra mocha latte or crumbly blueberry muffin. I find the menthol soothes my tired head, the sugar acts as a mini-energy boost, and there's that whole "if I fall asleep, I might choke on this" aspect at play too. And, an extra bonus, if you're at all like me and wake up WHEN class STARTS, sucking a cough drop will help to get rid of that awful morning breath.

Just an idea.
Good luck! Happy napping!