There are plenty of ways to eat healthily on the road if you truly have the desire and ambition. If you want to stop off a bunch of times at restaurants, choose restaurants that have vegetarian foods, low-fat foods, etc. Pick diners instead of fast food restaurants and ask for low-fat foods if necessary. Over time, you will learn how to make healthier choices. The internet is also a great tool for finding out ahead of time where to stop for food.
Many towns now have super health food stores.
You can go grocery shopping on the way if you run out of the foods you packed along. Plenty of people use road trips as an excuse to binge, eat junk foods, and treat their bodies poorly. Move over junk food. More and more people are committing to healthier lifestyles, and traveling on a road trip doesn't have to be a roadblock. Each time you take a trip, you'll learn new ways of eating more healthily along the road.