I patch jeans using an old scrap of denim from I don't even remember where. It must've been jeans that were irredeemably ripped (I don't do cutoffs). As I have cut pieces from the scrap over the years it has accumulated a long narrow appendage. It was too small to likely ever be useful, but I didn't a) need to cut a bigger patch than needed for a given job, because that just means more thread and sewing, and b) want to throw it out because someday it might be useful.
Someday arrived. One pair of pants had a gradually worsening stress tear at the top corner of a rear pocket.
The picture shows it already patched up, but these kinds of tears are not uncommon--although I usually haven't gotten them on my pants. Also shown is the source for patch material with the appendage mostly cut off. This is because on the backside, the patch looks like this:
The patch is small--only about 1 1/4" x 3/4"--but it's big enough to overlay the emerging rip visible in the top picture. Hopefully the adage of a stitch in time saving nine will apply here. There was almost no chance that little fragment was ever going to be useful, so it's nice that it found a use.
The repair itself was not that easy: as the top picture shows, I had to drive the needle through the top corner of the pocket itself, which meant punching through three layers of denim. I needed the thimble.
One thing that helped with all this (now that my eyes have reached that age...) was the big-eyed needles I got off Amazon:
They're not small-diameter needles, obviously, but they work okay for things like this. And maybe the broader end is a little easier to push on, in addition to the big eye being easier to thread.
Hopefully this patch holds up as long as some others I've done (still going strong after five years now).
