While the poster quoted by StbdD makes some very good points, especially about sensible clothing, two points stand out for me and reinforce what was posted earlier:
After immersion in freezing water your ability to help yourself is virtually NIL. The second, on the sensible clothing front, was the way the rescuers used TROUSER BELTS.
So, help yourself to help your rescuers, wear clothing that can assist in your rescue.