I have a few items I guess I would consider unique. I suppose this was the most fun in terms of significance and the necessary research. I purchased a collection of slides shot by a Pittsburgh based amateur photographer between 1970 and 1972. Those years are primary focus in my collecting efforts. This series of original 35 mm slides capture Clementes 3000th hit. They were shot from the third baseline and provide a perspective of that moment previously unseen. They also show the Mets outfielders throwing that ball in, Clemente on second, third, and scoring his last run and subsequently being greeted by his teammates in the dugout after that historic moment. For anyone interested here is the thread I posted six years ago about this addition to my collection.
https://www.net54baseball.com/showthread.php?t=220820