Non-spoiling bento?

I'm going on a trip sponsored by my dorm; the trip involves a long ride on a bus, and so I'm bringing bentos for the trip out. However, the last time I know I'll have access to a kitchen is on Thursday morning, and we return on an equally long bus ride literally all day Sunday. I'd like to pack at least some snacks in a bento box to avoid spending a lot buying food for the return trip - any ideas for recipes that can keep without refrigeration that long? >.> I'm thinking nuts are good, fruits with a thick rind if I don't cut them up... Alternately, I can buy things in Amsterdam - anyone know what kinds of things I can find there for no-prep bentoing? (If only I were going to Japan!)