Well I think that alot depends on the temperment of your kitten. We have a 3 month old boy bengal. We have family 8 hours away, and didn't have a sitter, so we brought him. It went very very well (even though he is very energetic!!)...Here is everything we did to prepare.
First we bought a carrier...the nice large gym bag type that is mostly holes...we bought it at petsmart. We also got a soft blanket to place on the bottom, and put his stuffed toy inside. Then we left the bag around so he could get used to it for about a week. (sometimes if he jumped in I would carry him around the house in it OPEN just to get him used to the movement in it...then we started taking him on small car rides (so that going to the vet wasn't his only ride!) At first he hated it and cried...but eventually he was better. I take him out of the carrier. If there are two of you..you can control him...if I'm alone he would stay in...Then when we finally took the drive, the first couple of hours he would cry a little, but he mostly slept. (highway driving is much more constant). We put his litter box on the floor and food and water. He only ate and drank when we stopped for gas...I had heard that he probably wouldn't use the litter...but after about 7 hours of being in the car I placed him in it and he went. I would test him out on practice runs. Trust me...he will eventually fall asleep on you the rest of the ride. Being cooped up will only aggravate him, so I would only do that if he doesn't settle down after a while...Good Luck!