You can chat on social websites online or you could take pictures as this are the best option. You can also take down notes on the different destinations and your experience as well. It would be sort of like writing for a blog on the experiences you had. Pictures and writing about the experience and the places you go to or pass through are the best things you can do for fun while on a trip.
There is a game my dad and I used to play... its called the alphabet game. You can only look at signs and things OUTSIDE of the car. Look at it as everyone has their own alphabet. You go in order and find letters and check off the letters you find... Q and J are the hardest... HAVE FUN AND GOODLUCK!( :