If your son likes Star Wars and you'd like him to practise his spelling/maths/etc, there are these Star Wars workbooks that our 4.5 year old son seem to enjoy. It's especially more fun when he's got a Star Wars pencil in hand. Might serve as entertainment during your travels. When we travel, I usually bring along a card game like UNO or a deck of playing cards, & a mini Etch-a-Sketch. What about Jenga for a game that you can all play and also helps with motor skills?