An A-Z character string written inside random page a book stored at a relative's house is a super easy way to secure a physical backup of your private key. You could even get clever and encrypt the key using some memorable passage of another book. Since the book passage is unknown to anyone else and be selected from a near infinite pool of paragraphs from the entirety of all published books, it would be impossible for someone to bruteforce even if they found the book where you stored the encrypted key. This would be an easy enough process to generate the ciphertext and store it in the event that you totally lost access to all of your electronics, online accounts, and home.

Sometimes it is: https://en.bitcoin.it/wiki/Cold_storage