S.N.
We packed our lunch each day.. made PB&J so that they wouldn't go bad, some fruit, veggies and snacks. We froze our water.. but I wouldn't recommend that b/c it didn't always thaw in time.
Even w/ out a fridge you can buy a loaf of bread, PB and apples/oranges... things that don't need to be refrigerated. OR get a big cooler, get ice from the hotel and just store the stuff in your room in the cooler (lunch meats, etc.). If you change the ice at night, before you leave in the AM, when you get home, etc. it will stay OK.
TOTAL waste of $$ to buy meals at the park... we had to one night b/c we stayed for the fireworks..... it was horrible and it cost us an arm and a leg. We did however buy a 'treat' each day like and ice cream, etc.
TONS of people do it so you won't look/feel out of place.
*** want to add.... bring your own stroller - they charge (in Fl) $20 per day per stroller! Your 5 YO may not ride in one normally, but they get SO tired he/she will want one there - as will you! Also - we brought our lunch in a back pack each day - just throw it over the handles of the stroller**