We brought a soft sided cooler and packed it with nuts, cheese, crackers, a PB&J sandwich (for the 4 year old's alternative lunch), baby food pouches (for the baby), grapes, and a couple of Luna bars. We ate breakfast in the room, and mostly didn't snack much. We did use our packed food to supplement lunches and for when we wanted to postpone (or skip) a meal to do more rides. I tried to stay high protein for real energy with the grapes for quick sugar pick-ups. We saved our empty calories for Mickey bars!
Packing the PB&J was great! We would have ended up buying lots of unnecessary and expensive kid meals. Instead, our 4 year old had a sandwich, cheese, and grapes, and we only bought a milk and an occasional soup or side veggie. He shared chicken or fish from our adult meals, too.