i got away with a lot of shit in college
i used to bring tupperware of tuna or pasta or anything for that matter and always sit in the back of the class and eat...sometimes id woof it done like the 5 minutes before the professor comes in class or even during class, 75% of the time they wouldnt notice, just the students, and for the real cool professors, theyd come back to my seat and ask what i was eating and say shit like "eww that crap stinks" and laugh and he'd go back to the fron of the class. i used to stink the whole back of the class room up with tuna and hard boiled eggs lol
protein bars are easy of course, also make a shake in between class and drink it during the next class.
as far as drinking thats easy, but peeing well hold it in and goto the bathroom as often as u can or do what i do, tell the professors that you have an overactive bladder and pee a lot and then they will not get annoyeed when u goto the bathroom during class.