Get an extra TripTik for the kids
Joel had a great suggestion for a little road trip geography:
An extra AAA TripTik for the back seat can stave off some bordeom and "Are we there yet?" questions. If you have time and your kids are old enough it's fun to have them pencil in a destination on each page of the TripTik. This creates moments of anticipation along the drive and a guarantee of regular rest stops with a sight or two along the way.
Keeping a crayon handy to cross off places already passed is also a way for your child to see how much you've made.
If you're not familiar with TripTiks, they are customized roadmaps the folks at AAA will put together for members. For free. Wonderful resource -- my parents used them on a few of my childhood road trips. Be sure to order your TripTik a week or two in advance of your departure date -- I imagine summer is a busy time at AAA.