since you don't have a way to keep food cool at your one job, i suggest going vegetarian so you don't have to worry about any meat products. in particular i'm thinking about what i make my daughter for her school lunches...a veggie sandwich with tomatoes, lettuce, cheese, and you could add sprouts or onions or whatever. mustard wouldn't spoil, plus no calories (or very few). made on a good, hearty and healthy whole grain bread...sounds good to me!
or, what about a cold pasta salad. i make a bowtie pasta with cucumbers, red onions, tomatoes, olives and a lite italian dressing; oh and i put mrs dash seasoning on the pasta before adding other stuff. for a healthier pasta you could go whole wheat. i used to put in green peppers too, but my kids always picked them out so i stopped adding them.