others have covered most of the points..but to give my 2c
Quells and pharmacy only type drugs are the most effective..if as stated you take them early and as per directions the worst you should feel is a bit sleepy.
Ginger is next most effective if for some reason you can't take medical drugs
the wrist bands work fantastic for some people, so wear em if you got em.
full stomach V empty stomach..I'm not sure either way, we do know that people that get on our offshore whale watching tours and eat pizza/burgurs/junk food just before departing hardly ever make it.
The main physical cause of sea sickness is the info your eyes and inner ear not agreeing. So if you read a book or watch the tv while on a moving boat or bus or whatever, your eyes tell your brain there is no motion happening, while your inner ear is telling your brain there is. The brain responds to this inconsistency by assuming it was something you ate..thus the nausea and the throwing up.
So watch the horizon..and get your 'sea legs' by moving with the motion of the vessel to minimize the movement of your head, that is try and keep it horizontal as possible.
tend to the center of the vessel where the pitch and roll is minimum
Also try do not work yourself up about it, some people can convince themselves to be sick.
if you feel sleepy, don't fight it..lie down and go to sleep.
and have a nice time in tassie