Mars Bars are a type of confectionary made of chocolate, nougat and caramel. On 1 September, 1991, when the trolley lady came to their door offering sweets, Harry Potter believed that he would be able to buy as many Mars Bars as he could carry; however, witches and wizards had their own set of sweets that did not include Mars Bars, and he therefore had to choose from the range of wizard sweets available.