Once I found a $10 not at the bottle shop with my mother and thought I was rich. I carried it all the way home in my pocket swearing I'd never tell her, that I'd go shopping or something. Then I told her and she took it.
Other than that once my mother found an envelope in a parking lot when we were going to the shops, found out it contained a couple hundred dollars, cold hard cash. With no name to identify it or anything, we had nobody to give it to. We kept it, divided it, and I don't know what we did with it.