you know you have to do too much when a boat pulls up to the island with one of those wakeboard towers and the gf says "why does he have an engine puller attached to his boat?"

Thats a dam good idea for one of those... Wonder how much weight.... never mind.

what everyone else has said plus a 12v test light....

I have lots of tools on board, it just seems that every time I need one of them, it's that one particular wrench that I left in my shed, but I always have my unlimited TowBoatUS card with me.

Any specialty tool you may need. I just put a kit together for mine and made sure I had what I needed to change L/U's on my O/B's if I ever needed to. It's a 15 min job but only w/the right tools and I refuse to pay someone $90. per hr for what I can do for free w/the right tools.
If you don't have them you have to just smile as you hand em the Visa card

Don't forget a battery pack good to have on board.

I keep 2 socket / wrench sets that come in the little soft black cases from harbor frieght. 14 bucks a piece. A hex set, a couple screw drivers, duct tape, zip ties, and wire snips and a couple flash lights.

I also keep a battery charger and this year i started to carry an extra battery as well. Ive had a couple problems last year with my battery dying when i was just sitting and had a hard time getting the motor fired back up.

Like most of us I have dual batteries and am anal about switching to one once stopped but w/my wars w/my 12 V coffee pots I have killed both of them before. I now mount the cables to the batteries via wing nuts.
A charge pack is a killer idea though and cheap insurance.
Our last trip to the Keys we stayed on the boat on the hook and I found out the hard way that my anchor light pulls enough amperage to kill a battery before sun rise! I've signed swapped bulbs to less amperage/candle power.

Buy the Kobalt basic hand and socket set or the craftsman one I think its about 150 piece set and a magnet for when you drop them in the water also carry some extra common nuts and bolts.....belts water pump impeller and prop hub kit if applicable also bring a wiring kit with a good set of dykes and strippers as well as a good crimper......butt connectors in blue and red are most common however you do need some yellow stuff here and there....good luck