The weather on the ocean can change in a moment. Dress for the coldest and wettest. You can always take off the layers, but you can't add layers if you didn't bring them.
 

Small cooler with food and drink. Hydrate often. De-hydration can occur quickly on the water. Bring plenty of beverages (Water, Gatorade, Coca-Cola, etc.).
 

Take anti sea-sickness medication two hours before sailing. If you take it when you start feeling sick, it's too late.
 

Wear rubber soled boots or sneakers.
 

Sunglasses, sunscreen, and a hat (Important).
 

Camera (Water-proof if you have it.)
 

Avoid alcohol and greasy foods prior to sailing.
 

If you are prepared for a great day on the ocean, you will have it.