The list is long, alas.
Tools. Many, many tools. Lots of screwdrivers - they seem to just leap out of my hands and bounce off the deck into the water.
Fasteners. Probably hundreds of dollars worth of stainless steel screws, nuts and bolts.
Prescription eyeglasses. Two or three pairs.
Dishes and flatware.
My favorite coffee cup when the handle just came off while I was dumping the dregs overboard.
A golf umbrella.
A four by six piece of Hyper Vent.
A couple of buckets
A Cell Phone
A foul weather coat
But the worst I ever saw was a middle aged woman on the docks who took off her rings and set them on the dock box lid to do some varnishing on the boat. Along comes her friend who opens the dock box to get out a brush. Several petite splashes and an "Oh my!"
followed as enough gold and diamonds to buy my boat five times over sank into the ooze at the bottom of the harbor.