Start with two or three two-litre plastic drink bottles. Drink the drink and wash and dry the bottles. If you have shopped carefully, you will find that you have bottles of slightly varying diameters.
Take the widest of the bottles and slice it in half at its middle. Then cut the central sections from the other bottles, discarding the top and bottom.
If you have judged matters well, you will now be able to assemble an extendable bread container, with the top and bottom of the first bottle joined by sections from the others. And the sections will slide, trombone- like, to fit the bread perfectly.