I would say NO to keeping a $100 bill if found some decent wad of cash I would return it because what if your school principal dropped it he or she wouldn’t be so happy if he or she finds out that you spent it on worthless junk. In fact what if the president of the United States sees you take it well let’s just say your going to be TOAST! Don’t let the devil convince you of taking the money because let’s just face it it’s not such a good risk. If you do take the money at least take it to a charity near you so at least help somebody in need.