Almost everything mattkab, skidgear and Cpseudonym (You're welcome!) listed plus:
12V rechargeable jump start battery with built-in work light - great for troubleshooting 12V items and a great light when the house battery leads are removed.
Large knife (or an axe) by the anchor locker for cutting away the anchor in an emergency. I have 120 ft of chain, but if I'm anchored on all chain in an emergency and need to cut away, I can cut the line in the anchor locker, then release the chain/line.
An inexpensive
multi-function tool for cutting wood, fiberglass, metal, plastic...just about anything on the boat with minimal dust and maximum noise.
A full set of electrical terminal ends,
hydraulic crimper, wire/cable and shrink wrap for field repairs and both Boat Unexpected Maintenance Projects (BUMPs) and Boat Improvement Tasks (BITs).
A
Clamp-tite tool to make replacement clamps from safety wire on the water.
A fairly large permanent magnet which can be lowered into the water to retrieve the critical tool unavoidably dropped into Davy Jones locker at the most critical time. (My hammer now has a wrist strap!)
My power drill has a 110 adapter plus an air pump accessory with needle valves to inflate bike tires, fenders, etc.
A 12V high volume/low pressure air pump to fill the dinghy and water toys. Higher pressure comes from the foot pump.