An odd one but relays for your trim. Cheap parts that are easy to replace on the water. I got stuck two weeks ago when my down relay went out. Thankfully it was at the ramp and not 30 miles away. Would be tough to get on plane if the engine was too high.
Manual release on tilt trim. Big flathead screw driver to actuate it.
Spare prop - just an old one I had replaced. Castle nut and cotter pins.
Wire of different sizes. Dikes and a few different terminals and butt connectors. Fuses.
Fuel lines.
A plastic straw. You can "grab" oil or seafoam with it and drip it where you need it.
Zip ties.
2-stroke oil.
HEET.
WD-40
Seafoam
Socket sets, both metric and standard, and extensions. A few wrenches, needle nose.
Normal safety stuff, air horn, whistle, lighter, extinguisher.
Spare plug.
Need a spare kill switch.
Probably should keep a big magnet in there.
Extra rope.
Light bulbs.
I've got a few motors that use shear pins, so a small baggie of those in a few different places, coats, blind bag, tool bag.
Don't forget your trailer.