Somewhere around the third hour of a drive, the cooler becomes the whole meal plan. A bag of chips is open, the coffee is gone, and the next exit has exactly two options: a drive-through or a gas station with a wall of candy.
Nobody needs a spreadsheet for that. A little bit of structure before you leave does more than any amount of willpower at mile 200.
Pack two things that travel well
You don't need a full cooler. A couple of items that survive a warm car — string cheese, apples, nuts, a sandwich, or whatever your grocery store has that isn't a mess — cover the moment when everyone gets hungry at once.
The goal isn't a perfect travel menu. It's having one decent option so the gas station isn't the only vote.
Don't make the rest stop a test
If the best available lunch is a drive-through burger, that's a normal travel day. It doesn't need to be balanced out with a sad dinner or an extra-long walk at the next stop.
A 10–20% deficit is a weekly-scale idea, not something a single highway exit can break. Two or three weeks of ordinary eating matter more than one afternoon of pretzels.
Watch the drinks, not the miles
The easiest calories to miss on the road are the ones you drink: a large soda, a sweet coffee, the second sports drink. You don't have to ban them. Just notice which ones you actually wanted.
Water in the cup holder solves more than most people expect, especially on a long, dry stretch of interstate.
Keep the bar low
Travel days are for getting somewhere. If you packed one reasonable snack, stopped once to stretch, and didn't turn lunch into a debate, the day went fine.
Back home, you don't owe the trip any compensation. Get back to your normal breakfast and let the week average out — that's the whole system.