Use current road maps and an atlas to plan out the trip before leaving. Don't rely on maps that are more than five years old. Stack maps in the order in which they will be used, and attach them to the car's visor with a large clip or rubber band so that they're handy during the trip. If the passenger in the front is up to the job, assign him or her to be the navigator. It always helps to have an extra set of eyes.
Children tend to get fidgety when locked in a car for extended lengths of time.
Bring along an empty tote bag for them to put their shoes and sweaters in when they shed them. This will ensure that the items are easy to find when it's time to make stops along the way. Pack a cooler with fun snacks for children. Juice boxes, string cheese and fruit snacks are some favorites. Another idea is to punch a straw through the foil top of a custard-type yogurt.