My dog van is air conditioned and separated into five individual caged areas so that the dogs can see and sniff each but not interact.....there's nothing more distracting when you're driving than a group of dogs playing behind you!  It is also a very good and safe way to introduce nervous dogs to the pack. 

I also carry a ramp for dogs who have difficulty jumping in the van, 10 litres of water, bowls, shampoo for those occasional fox poo encounters and of course towels