Abstract: A locking system for releasably holding open the opening of a plastic film bag, composed generally of a first locking element extending from the external surface of the plastic film bag adjacent the opening thereof and a second locking element extending from a shape defining structure. The first locking element lockably mates with the second locking element in a male-female fashion either by pressing them mutually together or by sliding one into the other. The shape defining structure may be a ring member of a sidewall of a trash receptacle or of a removable lid therefor, or some other structure, such as a free standing ring member which may or may not be of circular shape. The first and second locking elements may be configured in a number of different forms in order to accomplish the aforesaid mutual interlocking function.