Since other posters already suggested good ideas, I'd like to share one sort of "unorthodox" way of storing your mnemonic phrases.
Memorize it. Yes, you heard that right. A 12-word recovery seed is a lot easier to memorize that most people thought(though memorizing 24-word seed is still possible, just significantly harder). But I understand that this is definitely not for everyone.
this one,along with the google doc storage are the worst IMHO
both run the risk of losing access too easily
I have a very good memory,yet I stumble upon sites or accounts I created several years ago and passes for which I was supposed to rememeber
many I do,but there were a couple of frustrating episodes where I could not no matter how I tried
besides you can be injured (god forbid),suffer from a temporary amnesia etc.
you would not want your savings to be gone forever in this case