Oooh, actually working with the food yourself WOULD be hard. What I usually do to avoid eating vending machine food (although on a vegan diet, there's little if nothing I can eat from those thangs), is simply bag quite a few protein-happy (or sweet) foods with me. This is usually dried fruit, raw fruit (like, you know, an apple, pear, and orange, all fairly easy to carry around), nuts, seeds. All raw, easy things to have on hand and fill you up pretty well. Maybe a jar of almond butter (nut butters jarred can usually last a while in a bag un-refridgerated)? I LOVE the stuff by Mara Natha foods....
The best thing to have with you is simply something that you know you enjoy just as much as potato chips or pizza or soda or whatever. I'll be honest, I often love not-so-healthy food sometimes just as much as very healthy food, so usually the nuts and fruit will be just as good to me as the pizza and potato chips. *Shrugs* Bu' that's just me.
Best of luck!