Whether you're on a boat, standup paddleboard, surf board, this gear's for you. (We know some of you love doing this stuff in the cold... because you're cray... but the following is for people who love doing it when it's hot out).
Lightweight merino wool or cotton baselayer. Baselayers are the tops closest to your skin.
Shorts. Wicking. Spandex, cotton are OK great.
"Boat shoes", which typically have white soles. Also, water shoes, flipflops, or even barefoot.
Change of clothes and dry bags (to stow your clothes and towel. All dry bags float, however some are made from sturdier materials and will last you longer.)
Some boats and boards may require the use of personal flotation devices. PFDs will typically be on-board if you're renting/chartering.
Waterproof/flotation cases (for phones).