I'd say you need waterproofs (but not sweaty ones - it's still humid and pretty warm here) and windproofs, upper body only. Open sandals and shorts are best lower down, as there's so much water and mud lying around. On a boat windproof is the key, especially if you've been in the water and are wet. Wear baggy loose fitting clothes - they may make you look like a dustbin but they work much better.
Then for the occasional cool evening, or if you can stay clean on a golfcart, then lightweight trousers and something like a thin sweatshirt.
Still remember the hat and shades, as even when the air's cool the sun is no less strong.