The Floor Is Lava: And 99 More Games for Everyone, Everywhere | 
pickIf you've ever been driven mad by the phrase "are we nearly there yet?" then this book is for you! It has loads of ideas for games that don't require any equipment so can be played easily in the car on long journeys. Some are more fun than others but you can easily adapt them to your own rules. Loads of other types of games as well but it's the car friendly ones we've been trying out mostly.
LiseWorks We used to play the game where they had to find signs that had letters on them from A to z and you could not skip the letter. That took awhile to go through, kept them pretty busy especially when they letters were rare 2y