I can (as I say it proudly) do Disney with two kids for less than $30/day on food. And that is with a teen aged son who is a big eater. But, you have to plan it like a military operation.
We fly Southwest so bags are free. one of our suitcases is exclusively food and one of our carry on bags is a soft sided rolling cooler.
Packed bag: Loaf of bread, boxes of cereal, plastic bowls, peanut butter and jelly, tuna packets, mini donuts, poptarts, cans of pringles, apples, apple slicer or knife, ziplock bags, granola bars, nuts, cookies, random snacks. Mio water flavoring. I also take a small empty soft sided cooler.
Purchase half gallons of milk at resort.
Carry on: Lunch meat and slice cheese, yogurt sticks, cream cheese if I brought bagels in checked bag. Empty Quart sized ziplock bags.
After I go through airport security
I ask a food vendor to please fill two ziplock bags with ice and I put that in the cooler with the food.
Breakfast: Cereal, poptarts, donuts or bagels - in the room
Lunch: sandwhiches with pringles and cookies brought to the park in my little cooler - free Ice water with Mio flavoring.
Dinner: Alternate between $16 pizza at resort and approx. $45 CS meals.
I do splurge on refillable mugs for trips a week or longer but I only buy two (for the kids) and I drink water.
Now, with so many grocery options, I have given up my lunch meat cooler in favor of
Amazon Prime delivery but I still pack dry goods because who wants to pay $4.50 for a box of cereal when I can get the same box on sale for $1.50.