I have a Sit-In so the chances of keeping dry are a bit better than those on Sit-On-Tops. I will wear a light rain suit if there is a chance of rain and I wear a pair of wool gloves with the fingers cut out in the colder weather. I find that I can get these somewhat wet and still feel warm. I usually wear a pair of Lacrosse Grange boots ( a light waterproof pair) for when I have to tread in the water to launch and land at least until the water warms up, then wear a pair of boat shoes.
I always try to stow a dry towel to use when need.
I have been out with a friend on one of his Sit-Ons and wore a light pair of waders.
In the heat of the summer, being a little wet can feel refreshing. And of course I ALWAYS wear my Life Jacket!