More likely, you're trying to make sure the important information is available to a competent executor, and if it's not immediately available, it's in a form the executor can get it indirectly. You can assume the availability of friendly experts (including lawyers and application users), even if for a price.
If you're worried about someone digging up your treasure and walking away with it, don't
Here are the steps I follow:
1) Have a competent legal firm draw up estate documents and leave custody of the documents with them
2) Have a copy of the documents in the hands of the executor and family members. You can seal them, but make sure you have an executor who knows how to open and close accounts, pay bills, understand stock dividends, selling houses and cars, can talk to lawyers, and can get expert help when he/she needs it.
3) Get a program like WillMaker to help you document your assets and wishes (even if you use a lawyer to draw up the real documents).
4) As a matter of hygiene, don't be switching your money between custodians and accounts very often
And do all of the above every few years as circumstances change.
Stability and predictability are your friends.