We do this every vacation. I have some food allergies and we are fairly healthy eaters, so we try not to use too much processed food. If you have a car and can go to a grocery store - this is very easy.
Egg sandwiches (eggs microwave in about 1 minute, pre-cooked bacon and cheese on toast)
Rotisserie Chicken with a side of rice or grains (come in pre-cooked pouches for the micro)
'Nosh' meals - bread/crackers, cheese, tuna salad, or leftover chicken, hard salami, hummus, etc. sliced fruit
Lots of salads since the meals we buy seem to be short on veggies
PB &J on toast(great for taking to park)
Soups (if you like them) there are lots of fairly healthy brands out there
Burritos (either frozen or make your own - tortillas, re-fried beans, cheese, salsa)
I'll post more if I think of more.