I second the paper towels! We made a 1800 mile trip and our Frenchie (who is normally fine in the car) got car sick and vomited, a few times.
Also, I put beds in their crates, but made sure to cover the cushion part with a water proof liner (or maybe a garbage bad would work) so if there was an accident, I could pull off the top cover and change it out without having a wet pillow, too.
Kongs with peanut butter and kibble, were helpful, also knuckle bones kept them busy for some time.
Lots of breaks to get out of the car, stretch, play, explore, etc..
I also made sure I had a copy of their vet records in my purse, a picture of each of them, Microchip data, up to date, and a name tag that included our destination contact info (in addition to our home info)
I used ice cubes, from the cooler, to give them water while we were driving, so it wouldn't spill.
and ya, a first aid kit. Also, since we have a frenchie and were traveling during the summer, I made sure I had rubbing alcohol and extra water in case we had any overheating issues. (which we didnt, thank goodness) I am guessing this wont be a concern, for you, but its a good idea to think about what sorts of injuries your dog is prone to, when putting together a first aid kit.
Also, I made sure I had a sturdy utility tool that was capable of cutting through a collar, just in case. ( but this is probably my own paranoia)
Have fun on your trip! that sounds like a long one!