well, we've always gone the easy way out.
We drove to florida 4 times with the DD's- starting at ages 2 and 3. At that time, we had a tv/vcr combo in the suburban. Now they each have portable dvd players.
They also brought their leappads, gameboys and coloring books/crayons etc. The one thing I do not allow is eating in any vehicle (DD8 choked once while we were driving down the road) so we did have to stop every 3-4 hours so they could have a snack.
We stopped at big rest area's on 95, and would bring a kick ball, or something for them to run around and around and around with..
We've done it both straight through and with stopping overnight. Neither way was better for the kids, but stopping overnight sure was better for us adults!
I also went online and found touristy attractions where they could run around on our route- think- south of the boarder. i hate that place, but it was good for them....
I will sing praise for portable dvd players till I'm blue in the face, in april 04 coming home from WDW, we sat on the GW bridge in NYC for 4 hours. The only thing I heard from the DD's was "movies over, what are you watching.....im going to watch rugrats..." etc... They didnt even know we were stuck sitting- literally in PARK for almost the entire 4 hours. I cant say that i held up that well in that traffic...We also got a headphone splitter, so if they choose to watch the same movie- they can both hear it. There was very little fighting over movies. I set up a big stack in the morning before leaving between their seats, and they just picked and played them. I also had some new movies they had never seen waiting for the fighting to begin and break them out. It never happened, so they ended up just getting them whenever.
Another thing that I did- when we stopped overnight was to make sure the hotel had an indoor pool. I hate indoor pools, however, knowing they were in the car all day, they needed something to do before bed to tire them out. The pool was perfect! We also went to target, or
walmart at night, and walked around picking up stuff I forgot...that helped tire them out too.
Good luck, and just keep an open mind..
Brandy