Since it's summer and you're taking road trips I'd start by considering anything you'd normally pack in a picnic. A basic cooler with a few ice-packs can keep you from turning to fast-food places.
For some (sometimes unconventional) ideas, check out
this.Click adverse? look up the Portland Picnic Society as well as other picnic idea websites.
A few of my favorites for road trips/summer travel
Asian peanut noodles (can be eaten cold or hot and prepared days ahead of time)
An assortment of cheese, dried sausages, fresh bread and olives, hummus.
Salads without lettuce (they keep for days - any combination of cucumbers, corn, feta cheese, olives, beans, etc)
Slaw
If you want to get more advanced, pack a camping stove ('coleman style') and your options instantly open up to anything you can cook on a grill, from grilled sausages to veggies (zuccini, bell peppers, squash all work very well). Almost anything can be wrapped up into a tortilla and eaten with no flatware (try Marinated skirt steak with any fresh veggies, all grilled on a portable stove and eaten burrito style). Whole corn keeps great in a car and tastes wonderful when freshly grilled/steamed.
Bonus points - plan ahead and look for rest stops that have charcoal grills (many in the US do) - you can make lunch/dinner a festive stop instead of just a midway point before your final destination.
Iced Tea can be made by the gallon and kept in a large cooler - a nice and low-calorie alternative to sodas. Or lemonade/limeade if you prefer.
EDIT: fixed the link to direct to the correct website.