The bonesack is a large brown sack filled with bones worn in the back slot. It is a reward from completing the Rag and Bone Man wishlist miniquest. Contrary to popular belief it does not store bones. It can be switched for a ram skull helm by talking to the Odd Old Man again. This item can be enchanted to an enchanted bonesack after completing the Fur 'n' Seek wishlist.
The bonesack's examine info is a reference to the song "Love Shack" by the B-52s.
The "talking" bonesack is a reference to the H. C. Andersen fairy tale, "Little Klaus and Big Klaus," in which only little Klaus is able to "communicate" with a sack containing his grandmother's bones.