Since most of my plugs will float, I'd gather them up is they wash ashore so I'd keep a sinking one so I'd have atleast one sinking needle, but that is not in you scenario so I'll start over.
Cuttyhunk shall be the island(I hope I have good hiking boots on), and if I get bored there(which may take a few years, I'd swim over to the next island at slack tide
Tough decision on one plug but Bernzy's howdy in yellow would have to be my choice.
A close second would be a large ballarina since I made one that does incredible things and is very fishy, but if it has to be another members plug I would have to go with tagger for one of his large ballarinas.