An acquittance of mine recently spent a night hanging onto the side of his boat after wave and wind conspired to roll it over on him. He was spotted shortly after first light by another craft; he lost his signaling equipment. My thoughts...

Whistle, flashlight and small strobe should be on every vest; once the sun goes down, a cracked chemlight or waterproof light stick should be on every vest as well if your strobe doesn't auto activate on submersion, that way if you fall off and get run over by the boat you can be found. Grey and dark blue vests make me cringe- visibility, visibility, visibility. If you are going to rely on your phone, be sure it has signal, has charge, and put it in a plastic bag and tape it tight so you can use it even if gets wet. For a survival kit, the PSP or similiar, with a heatsheet (there isn't much similiar), lighter, flashlight- the basics, but not in pants pockets.