One way to cut cost on food at WDW, is meal sharing, pretty much you can share at most TS ( except Buffets or all you can eat)... just let your server know you will be sharing, and either they will bring you a plate so you can divide up or will do it in the kitchen for you... With that said Tip the server for more than the meals you shared, tip like you were tipping as if everyone order a meal.
Appetizer for meals... DH and I do this alot...lots and lots of interesting appetizers... you can always add a side salad or a dessert to share if you don't think that it will fill everyone up.
Quick serve meals are easily shared... When DD was at home, and a teenager, DH, DD and I could easily share 2 QS meals, and buy a extra drink, or a side salad or fries to add to it, if needed... As well you don't have to order a combo meal... if you want just order a burger, or just chicken strips...while its not shown on the menu board you can order it...
Spending a good bit of time on the menu board, and checking out the food pic's posted...you can tell what you can share at each spot, or when you are in-line look at what other people are carrying to see if it will work out for your family...
Bring water in with you... you can refill them as the day goes on... QS will give you water...
Snacks - that don't melt or are really messy... bring in with you things protein bars, apples, apple sauce pack's, mixed nuts, pringle's cans are great to keep chips and crackers and such from getting smashed... or bring along some cheap containers to hold items...
Since you are staying offsite... You might want to have a big hearty breakfast before leaving the condo.... starting the day out full is always a good option.
Check around where you are staying, for Fast Food, Pizza, Chinese, Burgers, to pick up on the way back to the condo in the evening...
If you are staying all day and are planning to make the fireworks, make sure to have some hearty snacks, sandwich fixin's back at the condo so when you return you can get something to eat without a lot of fuss...