Bag for picking mushrooms

Mushrooms should be picked with a basket. But it is cumbersome to carry a basket just to maybe find a mushroom.

Instead carry an ordinary plastic bag and something to expand the bottom of the bag. The same something should be foldable to be equally easy stored in a pocket. I am thinking of a spring in an O shape or a springy band of metal or a plastic surface or whatever. 10cm of twine and a found bendable twig should do the trick too.