Others in this thread have talked about safety deposit boxes and buried crates. I'd add that you can just give some trusted party a normal encrypted USB flash drive, and eliminate the risk of getting absolutely rinsed out in the event of a house burglary by splitting the password amongst an arbitrary number of your other contacts using the Shamir's Secret Sharing algorithm.
Others in this thread have talked about safety deposit boxes and buried crates. I'd add that you can just give some trusted party a normal encrypted USB flash drive, and eliminate the risk of getting absolutely rinsed out in the event of a house burglary by splitting the password amongst an arbitrary number of your other contacts using the Shamir's Secret Sharing algorithm.