All of the usual stuff, hats, glasses, a phone, shirt, etc.
But 2 notable ones...
The day I took possession of my first boat (Hunter 280), my son was going to help top off the fuel. Still not sure who pulled the fuel cap off (son or the fuel guy), but the chain was broken, and when someone let it go, off into the drink it went. No spare at the dock store. Broker finally "stole" one from another Hunter he was selling so I could get underway.
Then on my O'Day 322, was removing the Tac Tic wind sensor. My other son was winching me up the stick. Time to come down, wind instrament in hand, and my son dropped me (what felt like ) 2 feet. Of course, I dropped the wind instrament and she "floated" into the drink a foot from the boat. Tried to fish it out with a net, but just stirred up the muck. My son asks if I have a swim suit and a mask on board...I said yes, but the water is 50 degrees. Long story short, he dove in, took 4 tries, but he came up with the Tac Tic. I took him out for a nice steak dinner (and that was before I realized how much a replacement unit would have cost.
Greg