I'd say the biggest thing is being more careful and being much more diligent about wearing a flotation device. I think probably more people fall in around the docks than out in their boats. In the summer, that is no big deal and get's laughs. When the water temperature drops, it's life threatening.
We've never had to use them, only tried them out, but we do carry immersion suits and dry suits with us.
Our biggest time of risk is when getting in the RIB. We have a very rigid procedure at all times and make sure we're extra careful in cold water. It takes extra time to tie the RIB securely against the swim platform before boarding but it's a rule of the boat for us. No just stepping off into a floating and potentially wayward dinghy.
Collar. Throw Bag. Harness. Helmet. Gloves. Obviously rope. Life boat. Blankets. Warm drinks (non alcoholic).
Now, whatever you carry, you need to practice with. The key may be how quickly you can get into an immersion suit. How quickly and accurately the bag can be thrown. How quickly you can launch a life boat or dinghy. How quickly you can use your crane to lift someone in. Still with the desire for quickness you must get in a proper suit before jumping in.
I'm sure psneeld will fill in things I overlooked as he's had actual experience. I've just had training and practice and I know that is nothing like really trying to rescue someone.
If they're wearing a flotation device, you can probably rescue them. If they aren't the odds diminish quickly.
We basically have a kit in the cockpit storage.
And don't go it alone in those conditions. Carry a whistle too in case you're the one who falls in.