On our grocery stop, we bought a case of store brand (Publix) bottles water and a big pack of Capri Sun. Also bought breakfast items and snack items. Our travel party consisted of myself, my husband, and my 5-year-old niece.
Each morning, we packed about 4 bottles of water and a Capri Sun. If DN got hungry in the mornings, we gave her a grocery store snack from the backpack. My husband and I shared a water until we finished a bottle. Then DN could open her Capri Sun (in the mean time she could have water). As you probably know, you can't exactly put an opened Capri Sun pouch back in a back pack, so we would pour the remainder in our now empty water bottle.
At lunch, we would order a counter service meal for my husband and one for DN and I to share. Usually it was more than enough, but if not, we would eat some of my husband's food. None of us were ever hungry after lunch. The soft drink cups are huge, so we never finished those drinks, but we poured the remaining Coke into whatever empty water bottles we had.
During the afternoon, we always let DN get a snack, usually ice cream. She could never finish the whole thing, so my husband and I chose one of us to get an ice cream snack and the other just ate DN's leftovers. Granted, I felt slimed by the end of the week, but we saved a lot of $$!!!
We usually ate off property at night.