Container system and method for forming a knob in a container

A container system comprising a container, at least one (Previously Presented) coupling element, and at least one coupling system for releasably connecting the at least one coupling element to the container, wherein the at least one coupling system includes a male coupling portion formed on the container and a female coupling portion formed on the at least one coupling element, the male and female coupling portions configured to be releasably coupled to and uncoupled from one another, wherein the male coupling portion is integrally formed in a wall of the container and comprises a protruding knob that defines a head and an undercut, and wherein the female coupling portion comprises an expandable spring that defines a recess, wherein the at least one coupling element is couplable to the container by inserting the head into the recess to radially expand the expandable spring and allow the head to pass through the expandable spring, after which the expandable spring retracts into the undercut to engage the head and releasably couple the male coupling portion to the female coupling portion.