Dear Doctor, how might I best fabricate replacement roll boxes?

Cut the bottom few inches from a Cornflakes box and the same from a slightly larger Rice Krispies box. Place the roll in the bottom of the Cornflakes packet and then put the top of the Rice Krispies box over it for a perfect fitting lid. You can save on assembly time if you keep repeating the words “Cornflakes – bottom – Rice Krispies – top” while you assemble the boxes. Eating this much cereal to re-box your collection is very healthy indeed!