Oh, this reminds me. Has happened several times. I've kept something thinking it would be useful or needed one day. For 10 years 20 years a couple times. One day I think, "well if I haven't needed it by now, don't guess I ever will." Then one month later or less, I NEEDED it.
Should have done like my Dad. I had one of the first versions of the Honda Accord. In those days parts weren't just everywhere for them. Had a thermostat go out in mine. They were for some reason, not round, but oblong with the thermostatic part a bit off center. I take it out the local parts place doesn't have one. My Dad looks at it and says, that looks like one for a 38 model Buick straight 8. I said, "well great I'll see if they have one of those." He says, " you don't have to, I've got a new one in a box I never used right here." Now I thought no way will that fit a metric Honda. Especially being oblong. Now I don't know, maybe they copied the Buick, it slid in like a perfectly machined fit. I used it another 100k miles and it was in it when I sold it.