Bonine/Meclizine is good stuff. OTC Bonine has always worked for me.

Start using it 24-48 hours before you board your initial flight.

Take it every morning for the first 2 or 3 days of your charter, and if you have trouble with boat motion in your cabin, take it again at night. Eat SOMETHING for breakfast every morning, try to snack frequently, be sure to stay hydrated and that means keep a water bottle in reach all the time, 24/7.

You can get de-hydrated really easily early on a charter, with sun and wind , exposed skin, and in many cases warmer temperatures than you are used to. Alcohol makes you pee. De-hydration leads to electrolyte imbalance, which in itself leads to nausea , and thats pretty much a half-steppin, boot shufflin line dance right to Sea sick.
Being scared of being seasick is also halfway to being seasick. If you are scared of feeling ill, you can easily not eat, not stay hydrated, and put yourself right into the position you don't want.

Frankly, being sea-sick will be a lot easier, if you have something in your stomach to give up to Neptune. You will recover faster if you don't start from a position of weakness. Should you get to that point of "chumming over the rail," MAKE yourself keep sipping water, even if you keep tossing it. Have someone sit with you, and give them the responsibility of helping you remember to sip, sip sip. The absolute worst side effect of being seasick, is having no hydration to aid recovery.

It happens. It isn't anyone's idea of a good vacation experience, but one can actually do a lot to prevent it, and also to get over it.

Stay focusd on the things you can see and watch and participate in around you. Sit by the helmsperson, try to identify your course and your surroundings, get involved.