If you have a Sam's Club close, you can get the regular divided styrofoam meal boxes that the restaurants use. I think they're 100 to a pkg, and not terribly expensive. I have space in the basement storeroom to keep them, and a package of 100 will last us more than one season. Our d-i-l is the queen of the field meal, so I supply some of the "needs" and she does the work.

Since I'll be out of a job after next week, I'll step up and do more to help her out with that. She works from home, so it's been a decent arrangement so far.