The rest areas are also a good place to give your kids "travel treats" to relieve boredom. A favorite technique of mine is "the brown bag method". A week or so before the trip, I purchase inexpensive travel toys and small brown paper lunch bags. The first bag might contain a small brightly colored pad that the kids can use with their crayons. The second might have new markers or colored pencils. The third might have stickers to use with their pad and markers. The fourth might have a magnetic game. The next, a connect the dots book or a word puzzle. Each bag is then sealed and labeled one, two, three, etc. (Common sense is important here. If you give them stickers before the new pad, you can just imagine where they might choose to put the stickers.)
The bags are given to the child, one per child at each rest area, after they are back in the car and buckled in. The first child buckled gets the first bag. It's amazing how cooperative your children become, and you almost never have to tell them more than once that it's time to go, or to "buckle up". Surprisingly, sometimes the bags are the most memorable part of the trip.
I hope that some of these suggestions will help you and your kids to have almost as much fun en route as when you reach your vacation destination. Oh, and don't forget to keep the camera handy.