We did a similar trip a couple years ago. First, it might be worth it to loosen up on the tv watching since they can't get up and play anyway - not something I'd do on a regular basis, but this is special circumstances and they are stuck in a sitting position regardless (not that I don't totally respect your position on it). Second, my oldest got reward points for helping to entertain her sister (great to redeem later on vacation - or you could do another kind of reward system). Third, we had "grab bags" that they got to pull out from time to time throughout the car trip. They contained things like cheapy little toys, maybe a new dvd, snacks, a few had candy, etc. It really broke things up and made it exciting for both my girls. Even the little cheapy toys that would normally not be entertaining for long were novelties as they opened them and entertained them for a while. Good luck and have a great time! (Oh, and check into aqua doodles, they even have travel sizes)