Giving that wad of cash back will be the only thing I would do, because if I lost a decent amount of money like that I would be mad at my self, and if I took that money i would not stand the guilt of taking someones hundred dollar bill for a person that may need the money and god would never want you to take anything for a person. If i i was the person that took that money i would never be convinced that i I will ever get over the guilt. Don’t be a  big bully and take other peoples money give it to the cops or you parents don’t keep it.