Im probably missing some vital things but this is what I have together at the moment.
I'm forever adding things as when I do any work on the boat and can't find a suitable tool on board to do it and have to get one out of the shed I put one into the boat (within reason of course - fitted a new hatch this weekend and won't be putting a drill and jigsaw on the boat
)
Socket set
Open / ring spanners
Various screw drivers
Mole grips
Long nose pliers
Cutters
wire brush
Spark plug socket
Prop spanner
Selection of cable ties
Loads of gaffer tape !!!
Electrical tape
WD40
Pull cord for engine
Spare set of plugs
Spare prop and fittings ( would hate to try and change at sea! )
Spare fuses
Plus other odds and ends - wire, cable crimps etc