They're used as gifts for abundance in our festival called Alasitas, you can read more about it in the wiki page: https://en.wikipedia.org/wiki/Alasitas
I'd always wondered about this but never thought to ask!
It's for the alasitas where toys and miniatures of everything you can think of are sold. Even tiny bricks and cement bags! I have fond memories of going to them when I was younger.
I named my open source project ekeko based on the alasitas. I'm bolivian