What is the smallest amount that you will stop to pick up? ...a penny? a nickel? a dime? a quarter? a dollar?
My husband and I will stop to pick up a penny. He's done it for years (even though he is not generally frugal). I'm the frugal one, but generally am not looking down, but if I see it, I will stop to pick it up.
Careful though, I was in a parking lot and saw where someone had dropped a quarter and a nickel. I was so excited (yes, I can be that frugal) I stopped to pick it up and didn't notice a car was coming. My grown daughter pulled me out of the way but not without my 30 cents. I was in a crosswalk and the person should have stopped anyway.
My husband will also check the change return on vending machines (I pretend I don't know him) and around the cash register areas you can find change people dropped and left, also on the parking lots around the cars.