This is a natural and innocent looking prop, a mesh bag . The contents are always visible, but the bag is cleverly constructed to allow you to force the selection of small items that you put in the bag.
The bag could contain (for example) a deck of cards, shaken and mixed, and spectator reaches in to select a single card -- it is your force card. The bag could contain lots of crumpled up bills of many denominations. After various spectators reach into the bag and remove bills of differing denominations and serial numbers, the bills are shaken up and mixed, and someone takes one bill out, holding it
tightly in their fist. No one knows the denomination. But the mentalist divines the value of the bill, and for a kicker, he then divines the SERIAL NUMBER! Use just about any small object that you
can put a dozen or two dozen in the bag.