Telesack

A multi-size plastic bag could be made with the upper extension section(s) folded inside the lower bag. Each part would have two handles. By holding all the handles one holds the small bag. Letting go of the outside handles, lets a section fold out, and one is left holding a larger bag.

A shop need only use one sack type to then be dimensioned to the appropriate volume. A customer shopping in a second store could expand the Telesack for additional purchases.

The extension sections and extra handles can be breakaway-welded for ease of use. A variable, shopping bag for repeat usage could be made out of plastic or fabric with snaps or Velcro to hold the sections and handles flat.