I always carry a couple of wingnuts to use as spares. In fact, I've replaced all of my nuts with wingnuts. Always check for tightness before leaving home. Since I carry a multitool, I can always retighten as needed. I ran into a similar situation a few years back.

Even pop rivets loosen up and need to be checked. I found some very loose ones on my old tripping tandem. Similar storyline to you Mat.

I wrap tiny pieces of duct tape around the bolt threads below the nuts. It won't keep the nuts from working loose, but it will keep them from coming off the bolts and getting lost.

I always take a combination wrench too - the cheapest you can find will usually also be the lightest, even "Canadian Tire quality" is good enough.

one thing I never think to do is check the nuts on the bolts that hold the seat and thwarts on.  I could hear a little "clicking" going on occasionally as I portaged my boat this year - I use the front of the seat frame carried on my packframe

before I put the boat away after the trip, I checked the nuts, and even with nylock nuts, all of them were a little loose, so I snugged them all up.  So dry in Colorado that the wood tends to keep shrinking I think.

Yesterday, I took a different boat out to a local lake for a windy paddle -  I gave up after the first lap around the shoreline.  Unloaded the boat, keeping an eye on it sorta, just walking 3 paces or so up the landing to drop my pack and stuff but I turned my back for a second to set the paddle down out of the way - still too long, the boat got flipped and rolled once or twice before I could get back to it - had a real hard time keeping it from blowing away as I tried to load it on the truck (45# boat).   Anyways, checking it over for any real damage (just scratches) I noticed that that seat had loose nuts as well - all four on the seat and both thwarts, so I snugged them up as well.

Moral of the story?  check the bolts before you head up there - I didn't carry any pliers or multi-tool this trip, as there wasn't much I could possibly repair that needed tools.

Immoral of the story - never should have turned my back on the boat with the wind blowing so hard.  Maybe I could have jumped back to it in time if I'd been watching.  There was no place to tie it at that landing.

It was interesting to watch the people just showing up to paddle as I was loading up the boat.  One guy with a shiny new (at least looked new) wood stripper canoe - think it was a tandem, trying and failing to make headway in that wind.  there were four of those hobie mirage's, or whatever they call the kayaks with the bycicle drive/fins setup - took them 20 or 30 minutes to cover a quarter mile - without a paddle, they had a heck of a time trying to get the bow back into the wind, even with a rudder.  watch'ed another inflatable tandem kayak have the same problem, they couldn't get the boat turned into the wind; and another kayak trying to get out past a pinch where the wind was funnelling harder was at a dead stop.   I think I could have done better, but was glad I quit while I was ahead.  not too long a fetch there, but the wind was whipping water off the tops of the waves and gusting 40 to 50 mph