It's usually the smallest things that entertain our little ones. Another idea for the car ride is to take a cookie sheet (with the sides) and magnets for her to play with. The magnets will stay on the cookie sheet and the sheet also acts like a little desk. Crayons won't roll off either. These days you can find all sorts of magnetic books and things (even Mr. Potato Head).
We always like stopping at Cracker Barrels. They have the yummiest food and the little store has lots of fun stuff to browse. You can buy little things for her to keep busy with, borrow books on tape (to listen to and return at a CB at your destination) or little snacks.
Road side stops like picnic areas are fun to take breaks. If there's room, keep a basket of outside toys in your trunk. Frisbees, balls, bubbles, even a blow up beach ball (you can deflate when getting back on the road). Your little girl might like going on a scavenger hunt. Find the vending machine, a clover, a purple flower, a dog, a pink bush, etc. Play an alphabet game: find something that starts with A (apple), B (ball), C (car), L (leash), etc.
Small towns also sometimes have museums and historical places. Make it a point to read her the historical plaques to her. Or visit the local soda shop or dime store and talk to the oldest person there. I bet they have tons of stories they can share.
Anyway, I'm sure that you get lots more suggestions.
happy roading!
K.