I drive from wales to midlands or south coast of england a lot with DD's (3.6 and 20 months) have a bga in the front with you with non-spill drinks, raisins, bags of biscuits/snacks (tesco sell reusable crisp type packets which are great) Chuck one of them over your shoulder every so often. Things they can fiddle with are good, go to the pound shop and get crayons, small pads, stickers for them. I have some 'pockets' from GLTC here that clip onto the side of their car seats that I put crayons and stuff in. I also have Roald Dahl story cd's which last a good while.
I also take noisy fiddly toys that they like, DD1 likes calculators that beep DD2 likes mirrors, so they have their toys with them.
If you get anything new, always get 2, or there will be a fight <speaks from experience>
And for any journey over 2 hours stop halfway to let them run around and burn off some energy.
Ohh, and books. But be careful not to mix books up with drawing pads... And be aware that anything you give them will land in teh footwell after about 10 minutes and need fishing out. I pile blankets/coats in them so I can reach stuff and hand it back...
lol - know what you mean about the enormous crocodile. I give them a gym-bag each with a colouring book, coloured pencils (small packet, I have good reason for this) and as JB says some stickers - which inevitably end up stuck to the car but hey ho.... They have lap tray thingys, the tray with a bean bag underneatn, only the bargain variety, but it gives them something good to lean on and less chance to drop all their stuff / fight over it
I vote for the DVD player !! Drove to and from France last wk with 2.11 yrs and 9 mths DD's and the DVD player kept them both occupied. Had either me or DH in the back seat so we could hand things out and change discs etc (have a 7 seater so DD1 sat in 'boot' and could still see DVD). Trip took 13 hrs each way !! I now know all the songs in Alice in Wonderland and Aladin, and could recite Ratatouille from start to finish ! Good luck and make the most of this, I believe it all gets worse once they start asking 'are we nearly there yet ?'