We also do a grocery stop and the old styrafoam cooler trick!
This way I know we get at least some good cereal, milks, fruit and such during the stay. My girls love raw vegies, carrots, grape tomato, cucumber and even green beans so sometimes our afternoon snack is fruit and vegies. Don't get me wrong, they love the popcorn and ice cream! If we are at the resort for a pool break, all I have to do is put out the fruit and vegies with a little yogurt to dip and they go crazy!!
Lots of the restaurants are offering more healthy choices now including fruit stands at each park. Most counter service places will replace carrots or grapes for the fries, sometimes you have to ask as its not always on the signage. If both my girls get a kids meal I get one with fries and one with the carrots or grapes and they share both, compromise right!
We also find at sit down restaurants the girls (7and 9 btw) will often get an appetizer, a small salad or soup instead of the kids meals. Even a kid can only eat so much mac & cheese & hot dogs!
Have a great trip.
TJ