DonMichaels Said:
"For example, we use the same Amazon account, utility company accounts, bank accounts, lots of things. If I die, I want my wife to be able to login to all our accounts that we use for modern living."
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Handing Over Info:
A. Getting Other's Account Data:
If one passes away, then contact the site, informing them of this issue. Here is where you would go for Apple: How to Request Access to a Deceased Family Member's Apple Account - Apple Support
B. Keep a Journal:
If a must, keep a journal to have a hardcopy of this info. Store it in a safe place, and update iw whenever changes are made.