I would return things if I had an address or put the keys in the mailbox if it had one of those veteran's tags on it because they know people's addresses, but how can you return one earring? I would just leave that in place hoping somebody retraced their steps. I'm the kind of person who finds out I had something in the bottom of my grocery cart that I missed and I go back and pay for it rather than worry about feeling guilty about it for days.
My daughter forgot her purse on the back of a chair in a food court in another city one time and I told her to forget about all of her ID and start making phone calls to replace it all and report it. She received it back in a package in the mail. How great is that? Honesty is a wonderful trait in people and I like to think there are more honest people than dishonest people in the world.