I sometimes carry spare parts/items which I could never install/use myself. The logic in this is that it is sometimes easier to find a mechanic than to find the needed parts.
I once waited 3 days in a medium-sized city in Idaho for parts to repair my 20-year-old foreign truck to be shipped in. That's one reason that I now have a newer American truck.
Item to add to one of the the lists above: I think it is called a pocket chain saw. Piece of saw chain with handles at both ends. I don't build fires or cut down foliage to "improve" a campsite, but I have used this saw and a pruning saw to remove smallish fallen trees which were blocking an established road. No, never trees placed there as barricades. Just ones that fell.