Kids music to sing along to
Bag of new toys and things to fiddle with (doesn't have to be anything fancy, your $2 shop or op shop should be able to provide lots of random novelties!)
Snacks that take a long time to eat like rusks or cruskits
Give him a torch to play with - my DD LOVES hers so I save it for emergencies to keep the entertainment value!
Imitation games - get him to try and copy the noises you make and copy the ones he makes.

Sorry for the loss of your Pop and good luck with the car trip.