Hamish is right. That method works, and the more plectra/plectrums (depends whether you are Greek or not) you buy, the fewer you lose.
I once bought six at a bargain price at an auction, and then discovered I'd bought six dozen.
Now that I have 72 of them, I'm confident that even my Grandsons will always have one, even on to the third and fourth generation.
I wonder if there'll still be guitars in those days...
They'll still be arguing about the definition of folk for sure!
PS If you are Clive Gregson, and lost your plectrum at Biddulph. I've got it- taped inside the "Mischief" LP sleeve.