Image: Will © Image Source Pink, Jupiterimages

It isn't enough simply to sign a bunch of papers establishing an estate plan and other end-of-life instructions. You also have to make your heirs aware of them and leave the documents where they can find them.

Consider: At least 10 states have been investigating whether some of the country's largest insurers are failing to pay out unclaimed life policies to beneficiaries. California and Florida have held public hearings on the issue recently.

Insurers say they are behaving lawfully. Under policy contracts, they aren't required to take steps to determine if a policyholder is still alive, but instead pay a claim when beneficiaries come forward.

You can avoid such problems by securing important documents and telling your family where they are stored.

Jean Parr is grateful that her mother obsessed about the subject. "I really didn't want to think about it," says Parr, 54, a manager at the American Chemical Society in Washington, D.C. But when her mom died in 2005, she knew exactly where to look for the will, the key to a safe-deposit box and documents indicating her mother had paid and arranged for her own funeral.

The financial consequences of failing to keep your documents in order can be significant. According to the National Association of Unclaimed Property Administrators, state treasurers currently hold $32.9 billion in unclaimed bank accounts and other assets. (You can search for unclaimed assets at MissingMoney.com.)

Most experts recommend creating a comprehensive folder of documents that family members can access in case of an emergency, so they aren't left scrambling to find and organize a hodgepodge of disparate bank accounts, insurance policies and brokerage accounts.

You can store the documents with your attorney, lock them away in a safe-deposit box or keep them at home in a fireproof safe that someone else knows the combination to.

That isn't to say you should keep everything. Sometimes people hold on to so many papers that loved ones can't find the important ones easily.

In 2008, Jane Bissler, a counselor in Kent, Ohio, approached her then-87-year-old mother about organizing her documents. Because her mom was a widow with relatively simple finances and two homes, Bissler, 57, says she figured it would be a relatively simple task.

Instead, it took an entire year for Bissler and her mother to go through all of her papers, which included documents from eight bank accounts, utility bills from the 1950s and reams of canceled checks.

The two of them pared down the stash from four four-drawer filing cabinets to one two-drawer cabinet, shredding anything extraneous. Bissler and her mother visited banks and brokerages to ensure she was listed on all of her mother's accounts. Her mother died in May 2009.

"It would have been a total nightmare if we hadn't gone through it all with her," Bissler says. "It was that Depression-era stuff where you keep everything and hide other things." Bissler estimates that having the documents organized ahead of time spared them from ordering an additional 15 copies of the death certificate, and "years" of time.

Here is a rundown of the most important documents you'll need to have signed, sealed and delivered. You should start collecting these as soon as possible and update them every few years to reflect changes in assets and preferences. Some -- such as copies of tax returns or recent child-support payments -- need to be updated more often than others.

The essentials

An original will is the most important document to keep on file. A will allows you to dictate who inherits your assets and, if your children are underage, their guardians. Dying without a will means losing control of how your assets are distributed. Instead, state law will determine what happens.

Wills are subject to probate -- legal proceedings that take inventory, make appraisals of property, settle outstanding debts and distribute remaining assets. Not having an original document means this already-onerous process could be much more of an ordeal, since family members can challenge a copy of a will in court.

Rick Law, founder of estate-planning firm Law ElderLaw LLP in Aurora, Ill., says estate planners increasingly recommend revocable trusts in addition to wills, since they are more private and harder to dispute. "Every will is like a compass that points toward the closest courthouse," he says.

A revocable living trust can be changed anytime during your lifetime. After you transfer ownership of various assets to the trust, you can serve as the trustee on behalf of beneficiaries you designate. Provided you do so, there aren't any ongoing fees.

If your family can't find the original trust documents, you are "basically setting your estate up for litigation," says Duncan Moseley, vice president of Sanders Financial Management in Atlanta.

A "letter of instruction" can be a useful supplement to a will, though it doesn't hold legal weight. It is a good way to make sure your executor has the names and contact information of your attorneys, accountants and financial advisers. While the will should be stored with your attorney or in a courthouse, the letter of instruction should be more readily accessible, particularly if it contains instructions on funeral arrangements.

Also, make sure your heirs have access to a durable financial power-of-attorney form. Without it, no one can make financial decisions on your behalf if you are incapacitated.

Click here to become a fan of MSN Money on Facebook

Proof of ownership

You should keep documentation of housing and land ownership, cemetery plots, vehicles, stock certificates and savings bonds; any partnership or corporate operating agreements; and a list of brokerage and escrow mortgage accounts.

If you don't tell your family that you own such assets, there is a chance they never will find out. Moseley says in such an event, clients must perform their own detective work, watching the mail for real-estate tax bills or combing bank accounts for interest payments, for example.

File any documents that list loans you have made to others, since they could be included as assets in an estate. Similarly, keep a list of any debts you owe to avoid surprising your family. Wills and living trusts generally are drafted to include provisions for how debts should be settled, and creditors have a stipulated period of time in which to file a claim against the estate.

Make the most recent three years of tax returns available, too. "Looking at last year's returns offers a snapshot of what assets we should be looking for this year," says Lesley Moss Mamdouhi, a principal at estate-law firm Oram & Moss in Chevy Chase, Md. This also will help your personal representative file a final income-tax and estate return and, if necessary, a revocable-trust return.