We did adelaide to Gosford last Christmas with 18mo DS1 with one stop over night. Then after Christmas we drove to melb with a 2 day stop in Eden.
We've just gone to melb & back with 2y4mo & 6wko and took pretty much the same thing.
We took books he could 'read' by himself, CDs of kids music, fruit & vegies all chopped up and easy to eat, wet wipes, biscuits & crackers, lots of water, cars & other toys, coloring stuff.... But I think you said all that in your original post! Hope it goes well!

Oh & don't forget all the games you played in the car as a kid like I spy. DS1 is a bit young for letters so we do colours or size or noise instead.