My son loves to travel also! Now we use an iPad loaded with games like chess, speed, solitaire, math games, etc. When he was younger I made up many turn taking games with paper and pencil. Some games to try: pictionary (you draw and he has to guess), hangman, dot, dot. Before electronics, I had to be creative; when he turned 8, I caved in and bought him his first electronic device. Before that I said to myself, he's going to interact with humans, first! Lol. Using electronics can be interactive too, but it takes more effort.

Audio books borrow from the local public library! :D

I go to the dollar store and pick up a couple of new toys - cars, stuffed animal - and keep them put away/hidden until you are traveling. You know their attention span and how long something will keep them entertained. And a new something is always fun for kids. I also take snacks in small portions to stretch the time. Be careful with small crayons and loose paper - those things are easy to drop and roll and that might be something that will upset them if it gets lost. A dry erase board works for alot of things like tic tac toe, dots, hangman, drawing pictures. Some type of travel bingo is fun. For electronics, music, movies, games, books to read. My son is 10 now but even the small handheld games like solitaire, tetris that you get in the board game section of the store work and there are quite a few to choose from - Simon was a fun one and you just match the color sequence. I would take a small variety bag and if you get a couple new things, hold back one or two for the return trip.

During long trips gadgets come very handy. :) portable DVD for favor movies, educational leapster or leapad game. On a book bag bring favor toys, cars, train etc. crayons and coloring books, books to read, cards game etc.

You should check on Pinterest for busy bag ideas. It's a different activity every hour that's small, like coloring book and crayons in one, or puzzles made from cut up photos in another. Lots of ideas there.