Buck, I bought the booster pack after I didn't start one day and the boat next to me handed me his. When I left the marina that afternoon I stopped by West marine and bought one and like you, I now primarily use it for other people.
The few tools I do have on board keep rusting on me.
After my motor kept taking in water last year, I started keeping a spark plug socket, set of plugs and a spray lubricant meant for drying out moist wires and such. I actually pulled the plugs while rafting one day, turned over the motor & pumped the water out, sprayed the lubricant in all plug holes, had a few more beers, installed new plugs and finished out the day.
That's probably my biggest mechanical accomplishment so far. Thank god for Sea Tow.