We usually pack things like fruit, cheese and other snacks in a small cooler in the car. I purchase and prepare them ahead of time.
If I was planning to just pick them up along the way I'd look for trail mix (Planters has very tasty fruit & nut mixes) and possibly sunflower seeds. Pretzels are a good alternative to other chips. Many of our local gas stations/convenience stores (especially QT) have plenty of healthy options like fresh fruits, prepackaged fruit cups like DelMonte, cheese, fruit juices, frozen fruit bars and many other items. They began stocking all of these things because they accept our state EBT cards (food stamp cards) and they must sell healthy alternatives in order to participate in the program.
If you think creatively you should be able to find some good choices. Also, when I went on a trip with the girl scouts we found many stops had Subway restaurants which were another possibly healthy alternative.