Winter boating can be extremely fun and beautiful as well as very dangerous.
The water is cold and the weather can be unpredictable, not too mention there is less daylight should you have problems.
The best offense is a good defense, be prepared for anything, hypothermia will be your big concern.
1. Dress for winter. A dry suit may be your best bet with a fleece layer underneath.
2. Have extra, high energy food and water.
3. Have extra dry cloths, especially a fleece hat and gloves to retain heat.
4. Have some kind of emergency fire starter and small tarp for shelter.
Know the section you are paddling for access and egress points in case you have problems.
These items can fit in a small dry bag, so you folks kayaking should be prepared as well.
Most important, let someone know where you are going and when you should return.