>I have to secure a physical object that grants irrevocable ownership of my wealth?

Not really. Can be a file copied across dozens of public places that is well-encrypted (say AES256+Blowfish) using a key securely derived (say PBKDF2 with many iterations) from a random password you don't use anywhere else.

That said, if you do that, have a system that will drill you for that password weekly, or you will just forget it. And make sure this system can't be compromised to record your password as you type it.