We fly on Southwest so tend to bring a bunch of breakfast stuff with us as we can each check 2 bags for free. I have an insulated cooler bag big enough to hold 6 cans of soda, so I use that for things like yogurt and cheese, and a small ice pack. However, you will have a car, so you can make a grocery stop along the way! We always bring snacky-things into the parks with us; never know when the hangries will hit! Granola bars, fruit snacks, or snack mix (stuff like Chex mix or a mix with peanuts, pretzels, goldfish, etc) in a plastic bottle (like you'd get peanuts in) or a can, so it doesn't get crunched up in a backpack. We also bring "cuties" or "halos" tangerines; they hold up really well in a backpack and are very refreshing. With our own snacks we find we can share QS lunches, if we choose wisely (like the 1/2 chicken with sides at Flame Tree BBQ).
Depending on what time you leave the parks in the evening, you can place a take-out order from someplace like Olive Garden. We'd call it in on our way out of the parks and pick it up on our way to the hotel. OG gives you tons of salad, so we'd order an entree with salad, comes with free breadsticks, and then maybe a soup. It was plenty for DH and me to share. Another option, if you have a microwave, is the fresh, prepared meals. We bought these at Goodings, and they had everything: Meatloaf with mashed potatoes and green beans, pot roast dinners, grilled chicken with rice and veggies, etc. They were actual, not-frozen meals, that we could pop in the microwave. SIGNIFICANTLY more affordable than any meal in the theme parks!
