I would ditto the long pants/shirt and windbreaker type jacket...mosquito repellant,
poncho for a longer rain or one you can
throw on in a flash, flip flops for mud, etc.
(Slickers are good and warmer too but are
bulky to pack so just go with the layers,
and a cheap, compact poncho! Always take
more than one swimsuit...I just hate the
cold, damp, put on the suit routine! Enjoy
and breathe in some salt air for me. In
Phoenix