There are pressure points - one beneath your nose - another on an acupuncture point on your thumb - that can stop nausea. You'll have to research acupuncture and acupressure points to find out where exactly they are and how to stimulate them. Car or sea sickness is caused by your inner ear losing coordination - the mechanism of action is fairly well understood - you can take Dramamine - but you've got to take it about 20 minutes prior to riding. It may make you very sleepy as well. There are prescription nausea antiemitics you can take drugs like Zofran or try something more natural like ginger or peppermint.
They make "Sea Bands"... special elastic bands with plastic buttons that are placed on the accupressure points of the wrists. They really do work. Due to some health problems, I have intermittent motion sickness, sometimes even when I drive! Obviously, I cannot take Dramamine or Bonine for this, so I keep Sea Bands in all my vehicles. You can get them at most chain drug stores, for about $7. Well worth it, especially since they are reusable and you don't get the horrid side effects of the pills!