How does Charlie acquire a Wonka bar of chocolate between his birthday and the day when he finds a golden ticket?

Between the time of Charlie's birthday and the day when he finds the golden ticket, a span of about two weeks, Grandpa Joe confides in Charlie that he has been saving one dime as his personal hoard. He urges Charlie to go to the closest store and buy a chocolate bar to come back and unwrap. When they unwrap the chocolate bar, there is no ticket and they laugh in recognition at their own foolishness at thinking that they had had a chance to find a ticket