One of my favourite necklaces used to be an earring my dad found on the sidewalk :)
"Matching" single earrings is one of the things we do at the second-hand store where I work. If you find a sun and a moon, a cat and a
mouse, a skull and a pumpkin, etc, they can be grouped together for pennies. With the number of piercings people have these days, people often need an odd number of studs anyway (back when I still wore earrings daily, I wore 7). Through our recycling program, there is actually a way to divert single shoes away from landfill as well, by "matching" a left and right that are similar
enough, believe it or not. If we waste not, someone will want not.