You could add an appendix with printed, scannable, binary data. You could create a page with a bunch of QR codes. Martin Monperrus vouched [0] for Twibright Optar [1].

[0] https://www.monperrus.net/martin/store-data-paper

[1] https://ronja.twibright.com/optar/

Yes, I would definitely make backups on two or three different disc types.

Good idea, thank you. A DVD and SD card it is then!