In addition to leaving a spread sheet of information concerning all of your bills, I encourage clients to also print out a copy of the statements from their asset accounts. This is easily done when quarterly reports are received, either by mail, or via electronic format.
There should be a copy of your bank savings and checking account statements, your retirement account statements (401K, IRA, Roth), annuity statements, investment statements. It is less important to update these than it is to have the account information with your estate planning documents. This will give your agent (under your Durable Power of Attorney) or your Personal Representative (under your Last Will and Testament) a road map to your assets with the institution, account number and broker or agent.
Additionally, include a copy of all of your real property. Often times, clients have parcels of property in a different area of the state or in another state that their agents are not aware of. Make certain that this information is readily available.
In this way, your agent or Personal Representative will know exactly what you own, where it is located and the value of the property involved. It is only when an agent has this information that they can effectively do the job that you have requested.