Toys R Us has a rack full of magnetic playsets like
these.
They're very slim and fold in half to be the size of a magazine or smaller.
They have My Little Pony, Sesame Street, and lots of other characters available. You can find it in the "Imaginarium" section of Toys R Us.
If you belong to Costco, they have had some felt playsets that come in a clear plastic bag. Lots of different styles available.
At Target, they have these clipboard containers that are filled with colored pencils, markers, etc. You can find these in the crayon/art supply aisle. I love these for trips (car or airplane). I remove the insert and just fill it with the things I want. I use the pencils, but leave the crayons at home. Paper, color wonder stuff, etc. It keeps everything in one spot. It's similar to
these, but they come in red or blue filled with art supplies.
My snack advice is to just give them something new or normally "forbidden."
I also liked using a Snack Trap for finger foods like Cheerios, Goldfish, Cereal, etc in the car when my daughter was younger (1 - 2, she's now almost 4). And a juice box holder helps keep squirting juice at bay.
We only take 4-hour car rides (which can go up to 6 hours w/traffic. ahh traffic!), but even those can be trying.
Good luck!