A number of pieces that I wrote in the late 1960's and early 70's come to mind. In particular, two pieces for concert band -- Four Haiku Sketches and Ten Events for Band -- and several works for experimental theater. I'm also remembering an extended piece for double quartet (classical woodwinds and jazz ensemble) as well as more of my originals and arrangements for various kinds of ensembles. I did a lot of writing in those years!
At this stage in my life and in how my music has evolved, it is likely that I would no longer care for those earlier pieces. However, some of them might have stood the test of time and would be like meeting old friends again. Regardless, what's gone is gone. I am entirely happy to have all of the music that I have written since 1989...more than 30 years worth. When I think about the pieces that I no longer have, I can see how they served as a foundation for the music that came later.
UPDATE 2/9/2021: I just discovered that the score for Four Haiku Sketches is in the University of North Texas library. It is part of the Source: Music of the Avant-Garde collection. The score is in Series 2: unpublished scores. oversize, Set 1; Box 1 Barcode 711602. I contacted the UNT music library to request a copy of the score and will post an update when there is a reply.
UPDATE 4/30/2021: Happily, I received a photocopy of Four Haiku Sketches from the UNT music library. It is mind boggling that after 52 years I am seeing this piece again. Now, as I review the score and hear it in my mind, I would say that it still sounds fresh. At this point, I have spoken with the Director of the Composers & Schools organization (of which I'm affiliated) and she is enthusiastic about it. Both of us see this score as being like a time capsule from 1969.
Note: Four Haiku Sketches has been added to my compositions at the New Music USA Online Library.