I had a dog who went through a car sickness phase. Someone suggested giving him a spoonful of Pepto. Poor guy. He didn't like it. I can't really blame him--I always hated the stuff, too.
Every time we gave him any he would shake his head and the hot pink liquid would start flying. (I would recommend giving it to your dog on an easily cleanable surface). It got to the point that whenever we got the bottle out he would start shaking his head. He was a good dog, though, and accepted it well enough. Fortunately, it did seem to help. After a time, though, he no longer got car sick and we stopped giving him Pepto before car rides.