If you use a cake mix that weighs over 18 oz. you dont need to buy a box. I hav sometimes put the cake mix in a free small PO box to give it a bit of support and weight since some of the cake mixes are now under 18 oz. I just wrap them at home in brown wrapping paper before I get to the PO,. Someone here suggested using packing tape all over the box and then peeling off the stickers that the PO uses and just reusing the box and wrapping.