The humble brown paper bag, which you might use to carry lunch or lug groceries, is a remarkable contrivance. It can stand upright by itself. You don’t need an extra hand to hold it open while you fill it. Yet it readily folds flat for easy storage. Fitted with handles, it becomes a handy shopping bag.
All this comes from an ingenious set of folds performed on a tube shaped from a roll of paper to produce a flat-bottomed bag.