Personally, I use a disk image for the emulator Mini vMac that contains the old MacPGP 2.6 and a text editor. This is easily carried on a USB stick, and can be used on Macintosh, Windows, or Linux computers (and there are other ports). Further, the disk image should work on other Mac emulators. Of course, I'm the maintainer of Mini vMac - this might not be the best solution for other people.

Moving from analog to digital technology solved this. And you can include a checksum with your file to be quite confident that your current copy is identical to the original.