Get one of those cheap and cheerul multi toolkits for your boat keep lashing it with Wd 40 and replace it every two years . Its alot less depresing than watching real good tools sink or deteriorate in the boat; this one might suit you
spare bulb for your Navlights if you wear specs keepa spareold pair in your tub, and back up your mobile phone before taking it on the water.
I've got shedloads of this stuff (4) let me have a look and I'll see what I have got. I'm only keeping it on a come in handy for someone basis so you are welcome to it.
One point I also carry a clamseal and they look like they would come in useful iif neded but you must drive the boat home slowly to preventthe Clamseal from damaging the toob more also kepit in a plastic bag an wd40 it regularly cos the little pests like to rust in a flare pot