Rarest supreme item I can think of that was actually released and not scrapped or a sample is the 20th anniversary half cabs that steve caballero cut and duct tapped himself. 20 pairs.
Rarest item is actually the screen printed box logo tees Jebbia made at home to test box logo size when he still worked at Stussy, only 18 were printed, 4 of them the logo was deemed to big (destroyed), 2 perished in a mysterious fire, Harold Hunter is buried in another (RIP), Nigo has one in a cabinet/safe at home, Jebbias oldest son will receive one on his 94th birthday, Gonz has two, one he planted inside the L in Love Park Philidelphia, the other he wears cause he's too cool to care, another is in the electrical mains of the Empire State Building (cause New York), chrisvasilik has another (don't know the fuck how, rumour is he sold his soul), there is a rumoured secret for a Christies auction in the Prada foundation (Venice) for another on the 1st of April 2044 for the 50th year anniversary. Hugh Hefner keeps one so the Playmate of the year can have a nap on one as a prize every year. Three are still up for grabs, they are easily recognisable as they have a Supreme tag with the size marked as JJ on them (it is the mysterious Size between L and XL fucking everyone wants) Good Luck!