My wife also has the national parks lifetime pass. I get in for free as long as I go with her.
I discovered another surprise: The pass to sail at MIT that I filled out during my freshman year there is still valid! They still have my original card on file from when I first arrived on campus in 1969. I went sailing with my daughter two weeks ago while we were there for a reunion. They showed me that they still have a pass on file from 1937, but I doubt that any students who were freshman in 1937 are still sailing.