Bamse, the Swedish comic we subscribe has come with a number of games. They are often educational, cheap and small, so great for trips. Recently we got this letter game, which is super simple but easy to play while driving. Or at least this is how we play it in the car:
One player picks up a rectangular little sign from a bag. They have different categories on them such as a city, country, vegetable, male name, sport and artist.
Then the player picks up a little circle with a letter. Then we all first figure out which letter it is and then try to think of things that start with the letter in the said category, say you have a city with H and we come up with Helsinki, Helsingör and Hanko.
I suppose the idea really is to compete and see who is the fastest and collects most letters.However, with our kids who still are about to learn to read and the younger one is still in the process of learning all the letters, I think it is more suitable to do it all together.