Isn't that cool?
This is one of those times we get to reaffirm our faith in our fellow human.
Several times my wife or I have found money that the customer just before us forgot to pick up from one of those self check out systems and managed to catch them before they left. We even found out once that a small deli managed gave us back too much change, I think it was just $10, so we came back after the appointment we were stuck and and paid the man back. He was very delighted we made the effort, and we made a great new friend.
My wife once found over $200 that an elderly lady dropped and chased her down to get it back to her. The woman was very grateful, saying that was all the money she had to live on for the next 2 weeks, and would have suffered without it.
I mention this not to claim we are some kind of super people or something, but just to encourage others to do the same. These little acts can snowball into greater acts or a slightly better world in general. I personally was rewarded much more by doing something extra for someone, than what the money could have provided. We also do it to teach our boys what's really important in life.
Now, if I see money floating across a parking lot without an obvious owner, well, that sucka's mine! I'm still waiting to find a briefcase full of drug money that no one has noticed... Say hello to my new GAS fund!