Pasta salad has worked well for me. Made from dry or canned ingrediants that don't require refrigeration.
Cooked pasta (I use the tri color rottini or tortillini), some canned garbanzo beans, sundried tomato in a jar, artichoke hearts in a jar, sliced salami, olives, parm. cheese and some bottled salad dressing. Cook the pasta the night before and mix the whole mess in a giant 2 gal. ziplock at breakfast. Pop it in a cooler and for lunch I serve it up in some disposable paper bowls with plastic forks.
After lunch the disposable stuff is stuffed back into the giant ziplock which now serves as a garbage bag.