I do kid's meals at the counter service restaurants -- especially the chicken tenders -- for myself. Love those chicken tenders!
If you'll have a car, another thing you can do is take some snacks into the parks to help stretch a meal. I've taken carrot sticks and chips with us, then we get one meal and share it between the two of us. With the snacks, this is more than enough. We've even gotten away with sharing a kids meal on days we're not very hungry.
I also take one bottle of water with me on the trip and just keep refilling it at fountains and in the room. I drink water like a fish anyway, so this saves a LOT of money on sodas (and when DH is thirsty, he now drinks my water instead of buying a bottle of soda, saving us even more).
I know these aren't counter service, but maybe they'll help too:
Another savings I just read about, at sit down meals, is some places will do half servings for you. Someone on another thread mentioned this as they are dieting (I am too -- Weight Watchers since November) and this is a perfect solution for me. I'm not as concerned about the money as I am about the amount of food I end up eating or throwing away. But they usually charge you less as well so that's certainly an extra bonus!
Something else I've taken to doing at sit downs is order an appetizer and a side salad instead of meal. I can have some of the side dish DH gets if I want it and this is more than enough food for me and is much less expensive (looking at Yachtsman's Steakhouse, the steak dinner I would order is $31, but the steak appetizer is $11, salad is $8 -- savings $12 and about 1500 calories!). And then I have room for dessert (there goes the 1500 calories)!