I'd noticed a slow leak that I had checked out at the tire shop, but they found nothing. I dealt with it for months, filling the tire every 10 days, or so.
My brother, his son, and I decided to take off across Utah's West Desert in search of the Topaz Mountain Japanese Internment Site near Delta, Utah. At one stop to look at some very interesting rock formations my nephew said, "Uh, your tire is leaking." And sure enough, it was! Air was rushing from a small hole where a piece of metal had been hiding and my slow leak was going to cause real problems.
I popped open my tool box and found the cheapest tire plug kit I'd been able to find at AutoZone 5 years before. We tore it open, followed the instructions as closely as possible, and got a plug in the hole with 29psi to spare! Having that kit saved the day. (Or at least saved me from having to put my spare on...!)
In the repair process we bent the heck out of that cheap little tool and the first thing I did upon our return home was to buy the sturdiest tire plug kit I could find at AutoZone.
That plug was still in the tire, still holding air 15,000 miles later when the tread was worn out and I picked up new "shoes".