If you look at the boat as I look at aircraft over water, you might consider the contents of my aviation survival vest: Flotation vest, PLB, Radio, GPS, Flashlight, Chem lights, Laser flare, knife, DR PSP.

Obviously some of those are high dollar items and not everyone needs everything. OTOH, who's going to wear all that stuff in a vest while fishing? A lightweight ditch bag that floats could contain an excellent survival kit. Everyone still needs to wear a PFT; when stuff goes wrong it can go wrong fast.