Given the amount of thought and time I put into what I feed my children at home, it should surprise no one that I am not the sort of person who just stops at McDonald's for lunch and gas stations for snacks when we're driving long distances.
Not only would feeding six people that way for two days* result in a serious financial hit, it would also make everyone feel sick, because that is not the sort of food that we can eat more than once without physical discomfort.
I could write a really long, very detailed post about this, but what it really comes down to is passing out food in the car three stages: early healthy foods, middle less healthy food, and later treats.
So when we start out on a trip, the first things I give everyone are things like carrot sticks, snow peas, cucumbers, or cheese.
* Or longer. We drove four days from New York to New Mexico without stopping at a restaurant once. I made all our food ahead of time and had it in coolers.