Then I just covered with mac-tac (also from the dollar store). It fit perfectly on the kids laps in the car under their arm rests of the car seat. The mac-tac can be used as a dry erase board so you can bring dry erase markers and a cloth to wipe. Also bring magnet toys or letters. I made these plush coloured magnets for Isla since I was afraid of the magnets falling out of the plastic ones if (when) she chewed on them.
I got this fabric from a friend that is printed squares of colours. So I just had a layer of the printed fabric, a layer of white felt and a backing layer. I glued on a small magnet (dollar store) to the back of the felt layer and sewed around. I used fray check on the edges so they wouldn't fall apart.
Lilo liked the board for colouring books and Isla just liked the sound of things banging on it. Either way they were enjoyed and could be tucked easily away when they weren't being used.
This pretty one I made for one of the Pay-It-Forward people. I sent off 2 of the 4 gift, don't worry the other 2 will happen at soonish.