No one likes a growling stomach, especially not a kid on a long car ride. So for starters, time your meals carefully. If you hit the road at 6 a.m., don't wait until noon before you stop for lunch. Heck, even adults would be cranky under that scenario. Aim for reasonably filling meals every four hours or so.
Have plenty of healthy snacks and drinks on hand for the hours in between. You've got a lot of options, such as water, milk, low-sugar juice, cut up veggies and hummus, fresh fruit, string cheese, yogurt and nuts [source: Rogers]. An occasional cookie, piece of candy or scoop of ice cream is fine, but in general, stick with the healthy stuff.
Pack your snacks in a cooler before you leave, or buy them in grocery stores along the way. Don't assume you can purchase items as you go. If you find yourself in a small town, there might not be a supermarket that's easily accessible, and convenience stores usually have limited, often-unhealthy options.