I use Gmail for that. I send all such numbers, passwords etc. to myself, and archive them with a specific label.
Wifey knows the password, so hopefully, we will not die in the same plane crash

I know, this is less than what you had in mind, but it is practical.
Something with Gmail though, is annoying. I had an attached word document on my Gmail account. It was heavy on macros. Yesterday when I needed to access it, Gmail claimed that it contained a virus, and barred me from accessing it. I couldn't download it. I couldn't forward it to another account. I could do nothing (didn't try pop3/imap option though).
That's far from ideal. Store something in your account, and one day, out of nowhere, it will be infected if Google needs it to be.