I can remember being bored as a kid when we traveled. And I want my kids to have fun without looking at a screen the whole time. Every time we leave to go on a trip, after getting in the car, I give each child a surprise box. It's packed full of different activities each time we go on a trip to keep it interesting.
I bought old Rubbermaid VHS storage boxes at the local thrift store among other items like old calculator paper rolls for coloring. Any box will do. I like these because they lock and have a handle.
Make sure to put many options tailored for each child. These are my recommendations:
Crayons & calculator paper roll or pad of paper
Bag of Legos
Beads & string or pipe cleaners
Playdough or silly putty
Sheet of sandpaper & yarn
Free Car Game printables
Felt shapes with a large piece of felt
There are TONS of ideas! Scour pinterest or the internet and you'll find tons of traveling activities to keep your kids attention.