If you get seasick or motion sickness, bring dimenhydrinate. If you don't or aren't sure, bring dimenhydrinate. Otherwise you better pray and stare at that horizon like it’s the prettiest thing you ever saw.
I'm going to say this as someone who gets seasick, and motion sickness. Sometimes it happens. Sometimes it doesn't. Sometimes the waves are tough, so much that the engine stops cause its completely out of the water and everyone is puking up a storm. Now you can't exactly do anything if your captain abandons ship or someone throws you overboard a la Natalie Wood, but should Poseidon not exactly favor you, THERE IS A SOLUTION for seasickness.
The lesson in preparedness here, is that if you need it, it'll be there. If you don't, great, but it's one of those things better to have on hand while people are sloshing it up with martinis while you're laying face-down on the stern. That really doesn't sound like my idea of fun. Unfortunately, the Hong Kong harbor knows my stomach's contents first-hand. Keeping your boat in excellent shape is also crucial to having a great time fishing. You can go to website to find the best boating supplies.
This is nearly a must if you're going on a cruise or a long ferry. I would even say short, 20-minute town-to-town hops if you've got someone especially queasy with you. Plus, there's no better way to swoop in and save a pretty girl when she's down and out, amirite?