Good thread, and timely. When I get out in the boat in the cold weather, I've started wearing a semi-dry suit. It's kind of pricey, but keeps everything but your head dry, if you take a dunking. I've also started using one of the Spot locators. It lets me send an "ok" message with my gps coordinates to my wife when I'm on the river and there isn't any cell service. It also has "help" and "911" messages, but I haven't had to use them.
Be sure to check your lighter and flashlight in your ditch bag. Last year, during my pre-season test, I discovered that my waterproof matches were incompatible with the striker. It wouldn't have been pleasant to discover that in a difficult situation.
I carry this stuff in a ditch bag that I wear attached to my waist:
thin buck knife
storm waterproof lighter
rei waterproof matches in orange case
flint for matches in a small plastic baggie
Pelican small yellow flashlight
squeeze disposable flashlight
whistle
candle in a small plastic baggie
3 light sticks
3 tinder sticks
in waterproof dry bag
3 trash bags
small rain poncho
small emergency blanket