Energy Bars (Granola bars, protein bars, Luna bars, etc)
Hard Boiled Eggs
Drinks with calories (ensure, protein drinks, juice, milk, etc) - you can always put them in a thermous or water bottle.
PBJ (or other sandwich)
Crackers and cheese/pb
Really, the possibilities are endless!
I am sure your school has to make arrangements for other students who need a different eating pattern, such as diabetics. You could try to find out how these are managed and join in with this.
I have to respectfully disagree with snorker. As someone who has been in recovery, I can say that the last thing she probably needs is anyone calling attention to her eating habits or otherwise being singled out. It just makes things more stressful.
Pack yourself plenty of easy snacks and munch on them when you get the chance. All of the suggestions made by clickymouse are great. Peanut butter between crackers was one of my favorites during recovery (at the time I was in law school, and I had to do the same thing: pack snacks and eat whenever I got the chance). Trail mix is another great idea because it's easy to pack and take with you and nutritionally dense.