... Also, not a bad idea to bring extra clothes and stick in a dry bag inside the boat.
Anything you wear underneath
... some kind of running type shirt (ie Under Armor or the like). Don't wear cotton ...
Great points. In cold weather, I always bring a dry bag with extra clothes, and I never sail unless I'm wearing some sort of moisture wicking/quick drying shirt regardless of the weather. Once you start wearing those on the water, you'll never wear anything else. You don't have to buy the best brand names either, there are a lot of options now. I have a mix of name brand and off brand stuff. Some of the name brand stuff is a little nicer, but it's not twice as good even if it is twice as expensive.