I used to fly with a former ferry pilot who had the misfortune of ditching 2 hours out from Newfoundland. After 26 hours in an open liferaft he was rescued by a passing fishing boat.
His advice to me was:
(1) Keep your immersion suite and life jacket on - no matter how hot you feel.
(2) Make sure that your liferaft is suitable for North Atlantic conditions, i.e. it is covered has an adequate food and water on board, has a good (strong) sea anchor etc.
BTW he made another 20 ferry trips after his swim. He did, however, invested in the "Hilton of all liferafts” (his words).