As far as soups/stews, I usually freeze them before I go. They help keep other things cool as they thaw as well.

Sandwich meats, etc for making healthy sandwiches is good.

For snacking, lots of nuts and "Snack" veggies (sliced green/yellow/red peppers, baby carrots, celary).

I like the idea of hardboiled eggs. High protein things.

Any left overs from dinner the past few nights. I usually just make twice as much as the recipe calls for. Have it for dinner that night, then the wife and I have food while I'm gone (she works late and can't usually cook).