When I'm feeling industrious and pre-plan (typically early in the semester) I will whip up big batches of something on the weekend: jambalya, red beans and rice, chili, irish stew, etc. Then I'll freeze individual portions in plastic, microwavable containers. I toss one of those in a bag in the morning along with a pudding cup (I know, I'm losing serious gourmet cred here, but I love snack packs), a piece of fruit, and sometimes a string cheese. A quick minute in the nuker at school, and I have a damn tasty lunch. Late in the semester when I'm not cooking much it's a cold cut or PBJ sandwich with the same accompaniments.