Your pharmacist will be able to advise on the range of products available depending on the duration of the journey and any existing medication being taken. In addition there are several techniques that you may find helpful.
When travelling by car try to look forward out of the front rather than the side window and don't read. Ask the driver to avoid sharp breaking or acceleration and try to take corners smoothly.
On a boat it may be helpful to go to the centre or a lower deck where the movement isn't so great. Some people will find it helpful to close their eyes and lie down or fix their head against something like the back of a chair or wall.
Travellers who experience motion sickness on planes may find it helpful to sit by the window so they can see and understand the aircrafts movements.