Encrypting your disks will only keep people from reading them for a century or two. Technology from the future will be able to break today's encryption in a heartbeat, whether it's simple Moore's Law, quantum computing, cryptographic loopholes in today's algorithms, or something else entirely. So if historians from the future care about you, nothing you leave behind will be truly safe.
If you really want to mess with people from the future, do what Beale did, make up a bunch of bogus stuff, and throw it in with all your encrypted documents.
> Technology from the future will be able to break today's encryption in a heartbeat
I don't believe that's necessarily true. IIRC, certain algorithms would require computations involving every particle in the universe, operating for billions of years, to brute-force, provided that they are not actually broken. Will every current algorithm eventually be broken? Probably—but if not, they should be good.
Many of our current encryption algorithms can be broken by sufficiently powerful quantum computers [1]. We're still a while off from usable quantum computers, but they are coming, eventually.
If you really want to mess with people from the future, do what Beale did, make up a bunch of bogus stuff, and throw it in with all your encrypted documents.