Showerthought: a guy at a garage sale in Tucson sold me a $2 book on knots and it fixed my camping setup
I stopped by a garage sale on Speedway near my place two Saturdays ago and this older guy had a whole box of old paperbacks for a dollar each. I grabbed one on knots for two bucks just to be polite, mostly because he said "nobody wants the useful stuff anymore." Took it home, and turns out I had been tying my tarp lines wrong for like 6 years, which is why everything always sagged in the rain. Used a taut-line hitch on my last trip and the thing stayed tight all night for the first time ever. What dumb little skill did you pick up somewhere random that turned out way more useful than you expected?