+1 on wearing a PFD!! if it's bright wear it under a camo jacket.
Watch your swing. When taking a passing shot from left to right for right handed shooters (right to left for left) limit yourself to two shots. That third shot twisted off center can send you swimming in a hurry!
If it doesn't float, it needs to be leashed or floats attached... Don't ask me how I know

Go in a good 1/2 hour earlier than you think you should. This allows for all the what if's, and gives you time to really camo your boat with native vegetation. Take your normal camo blind material and weave grass and other plants in it to mask you and your gear.
Scotty rodholders work nicely to help keep your gun in position to shoot quickly.
These late season birds are getting SUPER WARY!! A small spread like 6 magnum size deeks and little to no calling will kill more birds. A month ago large spreads and calls were a must have, but the large portion of the migration is past us.
If you feel you must call, use a widgeon or pintail whistle. and use it sparingly if at all!
Hope this helps. Feel free to ask me any questions. I'm an avid kayaker, kayak angler, and duck hunter. I certainly don't have all the answers, but I know enough to help shorten your learning curve a bit. I've only got another week to hunt this season before I'm head to Colorado for 6 weeks, but if you'd like to come hunt the Nisqually with myself and a couple other quack yakers keep me in mind for next season!!
-Dick