My 2.5 year old has been on loads of long car trips thanks to our caravan. We are fortunate that he is an awesome traveller. Colouring books are a great idea, but at his age you might find he bores of them within a few minutes. Playing DVDs is what gets us through LOL! Also try and stop every hour or two so he can stretch his legs. Lots of different snacks to keep him occupied is good. Little containers are fine, then you can just dole out his snacks as you think he needs them. Don't forget to pack a big drink for him too. DS2 loves cars, so we also have an assortment of cars and trucks for him to play with. That's pretty much all we do, good luck!