Perseus carried Medusa’s severed head in the kibisis.
The kibisis was a special bag or pouch supplied for Perseus’s quest to obtain Medusa’s head. Perseus used divine equipment and careful planning to approach the Gorgon without looking directly at her petrifying face.
After the beheading, he placed the head in the kibisis and carried it during the rest of his journey. The head retained its power to turn onlookers to stone, allowing Perseus to use it against several enemies before giving it to Athena.
The kibisis is sometimes loosely called a sack, but the Greek myth identifies it as a distinct magical container. Perseus is the hero associated with it, not Heracles, Theseus, or Jason.