You are required to have:

•A receipt from the charity for the donation (does not have to specify value),

•Proof of the present value

•Information about the purchase date and purchase cost, or if this was a gift or inheritance, information about the date and manner you acquired the items.

You don't necessarily need a 30 year old receipt, but you need this information to determine the allowable deduction value.  If you are audited, you will need whatever proof you have for the auditor, the stronger your proof, the less likely the deduction will be disallowed.

If you donate tangible personal property that is put to a related use, you can deduct the current fair market value, for which an appraisal will certainly be acceptable proof of.  For furniture, a related use might be donating to habitat for humanity to put in the home of a needy family.  If you donate property that will be put to an unrelated use, you can only claim the cost basis or current value, whichever is lower.  An unrelated use would be the charity will sell the furniture to raise funds for other operations.