On a long car trip, plan to stop at least every two hours. Even if your infant doesn't need to be fed and changed, just getting out of the car seat and moving around can make him or her a lot happier. When you're rolling along, try singing songs. It's a good way to entertain your baby, pass the time, and keep your spirits up.
When it's time to eat, instead of the hassle of finding an infant-friendly restaurant, a picnic is often easier. Bring food from home or pick up something at a roadside supermarket.