I don't see why I'd need Solitaire. There is probably going to be something much more seriously wrong than someone tampering with my diary if I end up in a future where I am unable to get my hands on any simple computer I can make run a contemporary crypto algorithm.
Basic scenario is, I don't completely trust the safety deposit box, so I want to put something in there that can't be easily changed and rebuilt (maybe the reanimators botch something bringing me back and then go mess with my personal effects trying to alter the evidence that could tip me off to something being wrong).
I could just use a standard digital signature with a huge private key which I would then destroy. But I'd need to store the public key somewhere outside the deposit box, or else the attackers could just re-sign the forgery and replace my public key with theirs in the box. I could commit the public key to memory, but might forget it with brain damage. I could also try to leave it in some public archives, since the key wouldn't contain any information I might want to keep private, like the deposit box would.
The Scenario: Our protagonist estimates that present-day cryonics has around a five percent chance of leading to a successful revival. Since that's better than the zero percent chance if he doesn't sign up, and he can afford it, he makes the necessary arrangements. As part of those arrangements, he receives a lockable file-cabinet drawer, in which he can put any desired mementos, knick-knacks, or other objects; and which will be protected as securely as his own cryo-preserved body. The drawer is around one and a half cubic feet: two feet deep, one foot wide, nine inches high.
The Question: What should he arrange to have placed in his drawer?
Some of the more obvious options:
* Long-term archival DVDs, such as M-Discs, containing as much of his personal computer's data as possible. With slimline jewel cases, around 400 such discs would fit, which could hold up to around 1.5 terabytes. (Secondary question: Which data to archive?)
* Objects of sentimental value
* Objects with present-day value: cash, gold coins, jewelry
* Objects with predicted future value: collectibles, small antiques
* In honor of previous seekers of immortality: a copy of the ancient Egyptian funerary text, the Book of Coming Forth By Day (aka the Book of the Dead).
* For the purely practical and/or munchkin approach: a weapon, such as a fighting knife or even a pistol