We order from WeGoShop. We plan breakfast in the room everyday, so we'll order eggs, bread, milk, OJ, hashbrowns, butter, and bacon.
Depending on how much room we have in the suitcase, we sometimes order the nonperishables and sometimes pack from home things like cereal, pancake mix, coffee, cream, sugar, syrup, Nesquick, hot cocoa packets, muffin mixes that are just add water, and nonstick spray. If I can pack something like a partially used can of nonstick spray from home, then I don't feel so bad throwing it out at the end of the trip if we don't have room to bring it home. The grocery suitcase on the way down becomes my souvenier suitcase on the way home.
We also get frozen pizzas, cheese and crackers, grapes, place and bake cookies, pasta and sauce, and drinks.
The main thing is, think about how much time you want to spend in the room and then plan some meals that are easy to prepare. Don't forget to think about everything you need to prepare the meal. If you bring a brownie mix and then realize that you have to get oil and eggs at the gift shop, it's not so economical anymore.
We do breakfast in the room because it's cheap to cook and we want to be at the parks before rope drop and not have to stop touring until lunch. We do somtimes have things leftover that we have to leave, but if we spent $150 on groceries and saved $700 on restaurant meals, I'll deal with a little waste.