Wear anything, just get in there!
During our visit last September, we went eight nights in a row. I wore, in no particular order: Blue jean shorts and a white T with an American flag; both black and beige docker-style pants with collered shirts; chinos with a polynesian shirt; it really, really doesn't matter. The only people that got looked at sideways were either dressed WAY down (ripped jeans, dirty tee's) or to the teeth (tuxedos). Either way, they did get looked at sideways, but that was it.
I think "average" wear would be docker-style shorts and a decent casual shirt.
Pat