been there, done that, lots of times. You'll manage just fine. last car trip everyone got the stomach flu, at the time it was stressful sure, but looking back, you just keep going and stopping and going and stopping

but eventually you get there and in our case, everyone was over it once we arrived (24 hour drive, should have been 16) and after a days "rest" we were ready to go and missed no park time.
so I would say take a pack of lysol cleaning wipes under the seat, grocery bags for trash stash, and box of baby wipes for little ones. quarters for laundry once you arrive.
we have never had a DVD player in car until last year and never missed it at all. we do usually knock out 8-10 hours by driving over night. those window clings are fun to play with. colored pencils are good, no crayons, they will melt. audio cassettes really hold ther interest b/c it's something different, books on tape. always something new is a good bet.
just make sur eyou laugh t it all and don't let it turn into a nightmare. Remember this is suppose to be fun. We have laughed our way through some looong trips.
Driving again in a week, after flying last couple trips. with 4 kids, 2 teens, 2 toddlers. We will see if we are still laughing this time! 2-3 hours vs 20-24 hours. oh boy.