We always have 2 teens with us, so food can be quite an expense. We also stop at the grocery on the way in and stock up on fruit, chips, soda,ice cream, frozen pizza, etc. I also cook a VERY substantial breakfast each morning(OK, I LIKE to cook). Fruit, omelettes, toast, sausage, juice and milk. That holds everyone 'til a late lunch (about 2 or 3), which holds everyone with only a snack (French bread and cheese for adults, pizza for kids)in the evening.
We also budget in 1 or 2 special dinner meals during the trip. With Disney portions, the leftovers almost always make another meal. I also buy deli meats and sub rolls at that first grocery trip, make big sandwiches, wrap them tightly in the fridge. The boys can grab them if they are back at the room and hungry.
I was amazed at how much less we spend on food since joining
DVC. That available refrigerator of food comes in real handy - and that food is no more expensive than I would be buying at home anyway.