More off-grid, less failures. Private safety deposit box companies are excellent.

Banks aren't as discreet as private vault companies and it's not at all unlikely that a government entity would subpoena for your box contents.

Certainly a private vault company could be subpoenaed, as well, but for that to happen a prosecutorial or other undesirable entity would need to actually know you have a box there.

Set the box up, making as-few-as-humanly-possible trips to it, pay for it in cash for years in advance.

One caveat: I would use a bank vault for items like passports, documents, heirlooms, etc. Things that have no potentially-incriminating value or that government would have anyway (passports, DL copies, SS cards)