Something to eat (a lot of calories get burned up out on the water and sailing goes until 6:30).
A change of (dry) clothes.
Rain gear is often a good idea, and even on sunny days with lots of wind, you may see some spray.
fleece to go under rain gear
Comfortable shoes with good grip and a heel strap (not flip flops). We prefer closed-toed shoes like old sneakers, watershoes or boating boots.
As the whether gets cooler, woolen or fleece tight fitting gloves or sailing gloves will be needed.
Water Bottle, sunglasses and a hat are good ideas, sunblock.
Lifejackets (PFDs) if you have your own. PFDs are required for all SailMaine programs; SailMaine will provide PFDs if you do not have your own.
As the weather gets colder a woolen hat will be necessary.