My parents always tried to get small suites with minifridges so we could do breakfasts and lunches on our own - just cereal and milk and bread/meat/cheese for sandwiches. I'm also big on going to a regular grocery store, getting a loaf of bread, some good cheese, butter and apples and making that a lunch - you can feed a pretty big group that way much cheaper than fast food! If you're going a long way but want to bring perishables, you can also look into getting some dry ice for your cooler.
I bring my crock pot with me! We can be gone all day and come back to the hotel to a home cooked meal. I have a few standbys that are just dump and go like BBQ chicken just BBQ sauce & chicken. I shred it and have sandwiches with raw carrots. The best thing to do is to buy the crock pot liners so you don't have to scrub it in a tiny sink with no disposal. I bring a few Tupperwares for storage. Another easy meal is precooked chicken strips and a bag of Caesar salad mix to make chicken Caesar salads. Buy some rolls and you have a light healthy meal. I always book somewhere that has a refrigerator but also bring a hard sided cooler that I can keep things really cold in. Sometimes I have some precooked meals for the first couple of days that I bring with me.
Little Caesar's Pizza is almost everywhere! Can't beat that deal. Do you have a Costco or Sam's Club membership? You can find them just about anywhere, too. On our long road trips, we always try to find hotels that serve breakfast. Not just continental breakfast, but real breakfast. Many of them do. You may spend a bit more for the rooms, but with a family your size, it should definitely even out. We always pack a cooler in our car and take pb&j fixings, chips, and cookies. We try not to carry things that require ice, as that can get messy. But sandwiches, chips, and cookies for lunch and hotel breakfast means that we only end up eating out for dinner. When you're coming into a city, do a google search for restaurants that have kids eat free nights in that city. I hope that helps!
I love the crock pot idea. I also think just hitting a grocery store every day or two for essentials makes for easy meals: fresh fruit, bread, peanut butter, lemonade powder, build a trail mix, crackers and EZ cheese. Let the kids pick out a candy bar as a fun treat.
Here's what we do: a giant cooler - I don't know what you drive, but ours fit perfectly between the two front seats of the 12 passenger van. I make sandwiches and burritos out of the cooler. Fresh fruit fill in the gaps. Boxes of granola bars, bags of corn chips, yogurt cups... motels that serve breakfast!crockpot is necessary to our survivalIcecream cones at mcDonalds are the cheapest. (ha! just had to tell you that)We usually make at least one stop at Taco Bell - vegetarians can at least fill up there, but Chipolte and Subway work even if more expensive.
One thing we do before a road trip is fry up a bunch of chicken strips-lovingly named "travel chicken". They're good cold, warmed, in bread as a sandwich, with cheese, with BBQ, or plain and all of our kids love chicken strips. They're a good alternative to sandwiches, but wouldn't keep as long.