Paul Anka
Paul Anka was considered an "honorary" member of the rat pack. He was also a musician who hung around them whenever he could. As someone much younger than the rest of the pack, his nickname was "The Kid."
The Jack Pack
While their close friend John F. Kennedy was campaigning, the rat pack ended up calling themselves the "Jack pack" while they were with him. Peter Lawford was Kennedy's brother-in-law.