Every once in a while, there is a dog not yet accustomed to the car. The effects can be disgusting. Here is an article that may provide help next time pooch gets sick in the car.

[edit] Steps

Stop the car. Find the area where cars are parked. If on a highway, just pull over.
If the dog is in the back, get out of the car. You still might want to get out if your dog is in the front.
Locate the mess.
When you find it, wipe it up with a towel or blanket. Cover the spot.
For this step, you can either do this after you arrive at your destination, or while you're still pulled over. You have to clean the seat. To start, wipe it with some disinfectant wipes.

[edit] Tips

Be prepared. Bring some towels with you, especially if the dog is a puppy or has never been in the car.
Cover the area that your dog is sitting on. This will prevent the seats from being damaged.
A bottle of seltzer to pour on the vomit will help loosen it from the upholstery and make it easier to clean up.

[edit] Warnings

Children tend to get sick at the sight of the dog's mess. Tell them not to look at it. If they smell it, tell them to cover their noses.
You might have no other choice, even it it's nauseating.