I worked for many years in retail stores where finding valuables dropped on the floor or left on the counter by customers was an almost daily occurence. It would have been easy to deny having found something when a customer returned to ask about it, but I never did. I figure I got more benefit from their gratitude than I would have gotten by lying and keeping the loot.
If there's a Hell, I may go there, but it won't be for having kept some schmuck's dropped $50.00 bill or left-behind sunglasses.