Our dollar store has lunchbox containers with disney characters, you could fill it with special snacks to eat in the car or in the park.
My kids like:
Stuffed animals,
bags, backpacks, totes etc.
Candy or snacks with disney characters on it
Disney characters socks
Disney T-shirt
keychains (they can put it on their backpacks or beltloop etc.)
watch (can be useful in the park as well)
Okay I just read it again.
For in the car: You can google and print out car traveling games (licence plate game etc.)
disposable camera
art supplies with a clipboard
washable dry-erase crayons for the window or a whiteboard
craft kit (such as string art)
stuffed animals
watch with a stop watch feature
books