I've been fortunate in having others around me that follow the same food philosophies for the most part. That means nothing overly processed w/ odd colors, as well as high sugar, salt and ingredients I cannot pronounce. I take a grand I'm raising, her schoolmates, neighbor kiddos, and nieces and nephews with us on different vacations so being on the same page food wise makes all the caretakers' lives easier.
We pack a combo of fruit salad, dried fruits and nuts, celery sticks, carrots, and hummus packs w/ flat pretzels, squeezable applesauce, fruit leather for snacks. Sometimes I make homemade granola clusters but it depends on how messy the kiddos are that I'm traveling with. Nevah gonna happen again w/ my grand nephew, LOL. A longer trip will include yogurt, hard boiled eggs, individual salads with cheese added for those who like it. I generally make a large sandwich on crusty bread doused in olive oil that we share during road stops with a thermos of cold or hot soup since I'm not a fan of most foods served along interstate highways. Playing with making a gluten free black bean and chocolate brownie for our next camping trip; time will tell if it'll make the cut. If it works well I could see it being eaten as a car snack also.
Our car drinks are frozen water and unsweetened iced tea packed in bottles; they make nice ice packs too. Oh and we all love clementines/sweeties so we often bring a bag of them as well.