When we take a day trip we take bagels and cream cheese, cold pizza, orange slices and frozen juice boxes. The juice boxes are frozen on the trip there, but on the way home, they have melted. We keep everything in a cooler in the trunk while we are out of the car...the food is chilly, but not frozen when we go home.
When I was young, we always had bologna and mustard sandwiches on each trip. To this day, when I eat a bologna and mustard sandwich, I think of our family vacations.