My cat does not like to travel by car nor does she like to visit the vet.  The combined experience has a devastating effect.  As I was driving to the vet's several months ago, she first defecated, then urinated, and finally vomited.  The vet suggested that I put the cat in a pillow sack so she would not be able to see and become upset by her surroundings.  This worked a couple times.  The last time, kitty urinated through the pillow case onto my car seat.  She is very stressed by the whole ordeal.  Any suggestions would be appreciated.  She is otherwise a very sweet kitty.