Footwear: You get on the boat without shoes and/or slippers that will be removed before boarding

Luggage: A bag, preferably made of soft canvas, will do just fine. 

Steering the boat: Making yourself useful to normal steering activities is desirable as long as you know how to move. When in doubt, it is better to ask those who have more experience. Ditto for cooking and lunch/dinner preparation. The route will be established before departure, so you cannot ask to change it on the way or expect to get even short stops if not planned in advance. 

Water and electricity: It is a good idea to pay attention to the consumption of water and electricity. Bearing in mind that you are not at home, it is better to consult to optimize consumption while respecting everyone.

Seasickness: If you start to have symptoms, say it right away: you will be helped more effectively.