I took an inventory of everything on my boat that I would want to fix while floating and bought specifically to leave inside the boat. Some things require two of the same size wrench, so I have doubles of some.
Then, I have a dedicated toolbox that stays in the truck for anything major.
AN fittings
Hose ends
Spark plugs
Jet assortment
Silicone
RTV blue
Grease
Oil and filters
Gear oil