National and State parks are great stopping locations.
Instead of just taking the interstate or the parkway all the way to your destination, take byways and scenic routes! There's so much more to see.
Reading is, of course, a necessity for long car rides.
A camera is a must for traveling. It's no fun to see beautiful or interesting things without being able to save the memory. It's especially fun to scrapbook your photos after the trip - it's like reliving it.
It's always fun to stop at unique little diners while traveling. Don't just hit up the nearest fast food chain!
Monuments are not only interesting and often beautiful, they're great learning experiences.