AT Chase Manhattan Bank in New York you can rent a modest safe-deposit box for $30 a year. You can also get a box for $6,000. ''This is a very, very big box,'' says Donald Skelton, supervisor of safe-deposit boxes for Chase. ''We don't ask people what they put in them.'' And if that isn't big enough, Chase will rent you an entire ''secured room'' - located in the bank's vault area - for more money. Safe-deposit boxes. Brokerage-house boxes. Filing cabinets. Card files in the basement. How many storage files should a person have? And which financial records, if any, should be kept in them? If you have a safe-deposit box, a safe, or a filing cabinet with a key or combination lock, the general rule is that nothing of special value should be stored there unless someone else has access, financial experts say. A safe-deposit box is considered essential for anyone with valuables or documents that are irreplaceable. Safe-deposit boxes can be rented at most banks, with annual charges running between $25 and $50. Items that should be stored there include most certificates, including birth certificates, stock, marriage and car-title certificates. You should also squirrel away divorce decrees, death certificates, passports, military discharge papers, Veterans Administration documents, major contracts, deeds, your mortgage, adoption papers, pictures of your household goods and clothing for insurance purposes, and, possibly, rare coins. While many people store expensive jewelry in safe-deposit boxes, you should remember that the bank's insurance policy will not always remunerate losses from theft. Check with your bank. But homeowner's or tenant insurance will often pay for such losses. Many banks disallow storing cash in a safe deposit box. Life-insurance policies and wills, moreover, should be stored in a safe-deposit box, experts say, only if someone else, such as your spouse, or a close relative or friend, can gain quick entry to the box in the event of your passing. Check with your bank as to your state's laws. More than half the states now allow the co-renter of a box, such as a spouse, to open the box to retrieve wills, insurance documents, or cemetery contracts. But terms vary by state and by bank. In New York State, for example, a bank is required to ''seal a box'' upon notification of the death of a box owner, even if the box is jointly held, says Paul Sanchez, executive secretary of the New York State Safe Deposit Association, a trade group. A co-renter, such as a spouse, can open the box immediately after a partner's death to obtain burial instructions. But to get a will or an insurance document requires going to court to obtain a search order, says Mr. Sanchez. If you do keep wills and insurance papers in the box, ''keep photo copies somewhere else,'' says Sanchez. Many insurance carriers will not pay out death benefits until the actual policy is surrendered. If the box has been sealed, that could take weeks or months. The same problem arises with wills: If the estate of the deceased party must pass through a probate court, the court will not undertake a final adjudication until they have physically received the last written will. Thus, if your state does not allow instant access by others to a safe-deposit box, insurance policies and power-of-attorney documents should be kept in a filing cabinet, fireproof home safe, or other accessible storage container. Most experts recommend that a will should be stored with your lawyer. If not your lawyer, then it should be stored in your filing cabinet. The file could be simple - such as a box under a desk or in a closet. Or it could be more elaborate. But it should be a designated place known to others. If you have a ''living will,'' which is a document describing the disposition of your affairs in the event of incapacity, that should also be stored in this accessible place. What other documents should be stored here, in what might be called the ''accessible'' storage file? All major financial records, including homeowner, automobile, health, and disability insurance policies; installment contracts; investment account documents, including bank accounts, Individual Retirement Accounts (IRAs) or Keogh accounts; federal, state, and local tax returns; property tax bills and receipts; Social Security numbers; mutual-fund accounts; real estate records; stock options, warranties, and guaranties; gift and inheritance information; educational records; and recent payroll stubs. Securities, that is, stocks and bonds, can always be stored in your safe deposit box or at a brokerage house vault. If you lose or damage them, they are hard to replace. Storing them with your broker, if you have one, can make sense, since securities held at brokerage houses are insured up to $500,000 by the Securities Investor Protection Corporation, an insurer. And some brokers even pay for additional coverage. Tax lawyers generally advise clients to keep all supporting tax documents for at least three years, since audits can occur at any time within 36 months after you file a return. The IRS, however, can conduct audits whenever they believe fraud may have occurred, so some tax experts suggest that your most important tax materials be kept for much longer periods of time. Also retain information showing a capital gain on your house. Finally, if you believe that a deceased relative had a safe-deposit box somewhere, you can pay a fee to a ''search'' firm to locate it for you. Your bank can usually find a search company. In most states, a search must be concluded within a set time period, since banks can eventually gain access to an inactive box, such as after a year. Cash is usually remitted to the state. And after an additional waiting period - three years in New York State - the bank can auction off the remaining contents of the box.