We take long car trips and airplane trips every year as our families are scattered all over the world (literally), Some of my favorite ways to keep our kids busy over the years have been:
-felt board: you can buy a ready made kit or if you are crafty, cut out shapes of felt such as cars and traffic signs or animals and create a felt background
-travel bingo: for the younger one, find simple things such as barn, red car etc. to search for,older ones can find smaller signs or license plates from different states
- if your youngest sits by a window, buy window clings (we do this on airplanes too)
- wrap small presents (dollar store) and give each child one either once an hour or what ever time you decide. these don't have to be anything fancy, but my kids love opening presents, works also as a bribe

if they get restless..
- when you find books, dvds or videotapes on sale, set them aside. this is the perfect time to watch a new movie
-travel size magnadoodle, etch a sketch etc will also work if you can find them
Traveling in the care is easier than flying as you can bring more things with you and noise (as long as you can stand it) isn't as big of a deal. Enjoy your drive!!