We have some vtech books. They play music and do ABCs etc. I think they are majorly OS for LOs so keep them for car rides since they tend to be SO boring LOL
We also used snacks, as you do, and a sippy cup, sing songs, and let her pick toys to bring in the car. If it's possible, keep the toys/books (we bring reg. books as well), etc. up by you or your partner and then you can offer them one at a time when the novelty of the last item wears off.
I will say....it def. gets better! DD hated riding in the car around that age. Esp. if it was a longer ride (longer than 15 mins. LOL). BUT now she can handle most rides that we take, up to about 2 hours. She knows that we WILL get there at some point so has more patience.
HTH
Good luck!