Well, we have a DVD player for the truck, and we just spent 4 hours with the kids watching (us listening) to Shrek and a couple of episodes of The Dukes of Hazard (an old American TV show from the early 80's. DS2 loves it!). Literally just spent. We got home 30 minutes ago!! LOL! We got the DVD player when DS was 22 months, was a true lifesaver when we drove to see my folks (two ENTIRE days of driving with three kids, so think about 10 hours or so a day).

Other than that, lots of snacks, juice, and music. One of you could sit back there with her and play and read books. Favorite toys (play cell phones were my kids' favorites) are good, too.

Good luck!