During the Winter months, the must haves are...
Waterproof rain jacket
It's important to wear layers. There are some nights when it seems that you will freeze to death, then you start paddling and cannot wait for a break in order to take off a layer or two.
Some personal favorites:
Ski-pants (or a waterproof shell over long underwear), long underwear, dry-weave pullover and a warm beanie.
Remember to bring something warm to change into for that drive home too.
Honestly, once you're on the water, thoughts of what you are wearing will fall back in the list of considerations, but it's always good to ask. If you are unsure about anything, please feel free to contact email@example.com and we'll get back to you ASAP.