This is a natural and innocent looking prop, a mesh bag with a handle .
The contents is always visible, but the bag is cleverly constructed to allow you to force the selection of small items that you put in the bag.
A flat circular plastic box has one die inside. The magician shows this, then puts the lid on the box. He tells the number which will be on the top surface of the die, then he shakes the box, opens it and shows he is correct.