I'm sure most of us could actually list loads of things if we really put our minds to it.
I have trophies with my name and dates on. Ditto certificates.
Then there's my credit cards which I sincerely hope are unique.
But trying to enter into the spirit of the question, I have a copy of Wilbury Jam's first album, "A Good Spread" signed by all 3 members of the band "to Stan". Stan was the landlord of the Potters in Burgess Hill, where they all went drinking (and allegedly still do) at the time that they started out. I went to their 25th anniversary concert a while back (which made me feel old, as I went to many of their early ones at the Concorde, too!).
I have a tape of an early U2 BBC "In Concert" that ends with half of the song "Rejoice" (before it was released on vinyl) before Gary Crowley jumps in to end the broadcast. According to the U2 forum I visited, no-one has ever come across a live recording of "Rejoice."
I'm not sure how right they are about that though.