How about a small white board & some dry erase pens ? They could play hangman, tic-tac-toe & the game where you close in the most squares to win. The name has slipped my mind!
I don’t know how old your kids are, but mine (older, know their parts of speech) love Mad Libs!
Another thing my nutcase kids like to do is make signs that say “hi!”, hold them up in the windows & wave at people as they pass. Please bear in mind most of my kids are 11 & older (I have a 3 yo, too), that’s why they’re nutcases. These are teenagers doing this!
I guess it could be worse!
Also, I’ve always packed colored pencils instead of crayons. Pencils don’t melt! I keep a pencil sharpener in my things.
My family is taking a long road trip next month (Colorado to NW Florida), so I’m in the same planning place as you. But, most of my kids can be in charge of their own entertainment!