We all paid big tax money to send people up into space for a couple of decades, and almost half of the early astronauts spent a lot of time being sick from weightlessness. So a major effort was made to research motion sickness for several years, and everything that you can think of was scientifically tested.
In the end, it was found that it was important to start out at least eight hours before launch with some type of medication, the ingredients in dramamine and similar drugs, a half-strength dose that would prepare the body's balance mechanism. Best of all was a light dose of scopalamine, available either in a compounded pill as mentioned, or in the dime-sized patch worn behind the ear.
If you wait to get onto the boat, plane, whatever and see how you feel, you are already behind the curve. If you have any sensitivity to motion at all you should be proactive. And then don't put a lot of liquids into your belly and let it slosh around. Stay up on deck where you can see the horizon and get fresh air.
Ginger, wrist pressure bands, a whole bunch of things seem to work for some people. But the only things that are scientifically proven to work are a couple of medicines in the bloodstream.
