I found some of these uncancelled covers with the USPS inaugeration stamp (Scott 1396) stamp affixed. Upgraded them to current postage rate and took them down to the PO for a hand back cancel! I may or may not add some printer information indicating 45th anniversary cancel. Just something stamp collectors do to pass the day.....
(I did get two different cancels out of the deal!).....

Addenda: I still have 3 of these prestamped covers left, so if I live 5 more years I will get a 50th anniversary cancel!