I forgot how much we actually spent on food for our family of 6, but it was a lot less than I had thought we'd spend. You didn't ask for tips, but I'll give them anyway.
We went to the grocery store and bought breakfast and snack food (muffins, little cereal boxes, fruit, etc) and ate in the room most mornings. That worked out well--while some were getting dressed and ready others would be eating. We had a plug-in cooler that we brought since we drove. Some people buy a styrofoam ice chest. I've also used a soft-sided cooler in the room when I've flown.
We brought some snacks into the parks.
We used insulated water cooler jugs (not the big ones, maybe 1Qt), filled with ice and bottled water (I'm not crazy about the tap water) and brought extra bottles of water in with us. We had a stroller to carry everything--I don't know that I'd do this without the stroller, to this degree at least.
We got a couple refillable soda cups. Like DM said, they are expensive, but can be used the entire stay for reduced price drinks. Again, we had the stroller to carry everything on and in, which helped.
We weren't fancy eaters and ate counter service most of the time. My kids are big eaters, though (I have a 13yo boy who seems to never fill up), so the snacks really helped keep the food bill down.
T&B