I highly recommend any of the Hank the Cowdog audio books. They're hilarious and well told, and they'll entertain the entire family from you all to your kids.
We took two- day road trips when our kids were small, and this was the one thing we all enjoyed together. My adult kids still quote lines from the stories.
I found my kids liked their own, familiar toys over new things - action figures, Hot Wheels, etc. I let my kids pack their own back pack that sat at their feet with the things they chose to bring.
