I'll preface this by saying that I don't like to cook very much anymore, but what worked well for our last large family group was to load up at Costco (on Orange Trail) at the beginning of the trip with:
simple breakfast foods - cereal, milk, bananas, juice, bagels
ready-cooked rotisserie chickens, brisket, bag of potatoes (to microwave)
and frozen vegetables
lots of bottled water, other drinks
Then we stopped at a regular grocery store for fill-ins: butter, cream cheese, jam, onion, etc
On the first day it took me about 10 minutes to put what would become a bbq-flavored brisket in the oven, then I let it slow-cook for several hours.
We ended up with plenty of stuff for really good sandwiches all week, plus a couple of meals that we decided in the moment to have "at home" rather than out.
We really like to eat out at table service restaurants, but counter service meals when the crowds are heavy can get old and annoying fast, and ordinary simple breakfasts at WDW are expensive and I think consume time better spent on rides.
Just one opinion, but this worked for us.