Not to be obnoxious, but here are some things I keep in the cockpit, as I try to not leave it anymore than necessary:
1) pee bottle ( a big Gatorade does fine)
2) spare vhf, on and in a charge cradle
3) soup/lunch in a thermos
4) an alarm of some type for reminders (position log, sunscreen app etc)
5) my Spot, which I use to check in once an hour, on the hour, with my float plan holder (buddy or wife)
6) more line bags than others(I hate lines under foot)
7) Binoculars
8) A red handheld, low power, laser.
9) two handheld gps, with one below in an oven/faraday cage.
I also have a pilot style checklist for set up and take down, along with a paper maintenance log, as at the end if these trips I'm dopey tired.
All in all, fatigue scares me more than other drivers.
Jeff