In addition to the receipt (which does not have to specify value and almost never does), you are required to have a detailed list of items donated that includes when you acquired the item, how it was...
See more...
In addition to the receipt (which does not have to specify value and almost never does), you are required to have a detailed list of items donated that includes when you acquired the item, how it was acquired (purchased, gift, etc), when it was donated, the condition (good, fair or poor), the fair market value, and a description of the item with enough detail to be able to determine the value. Without that detailed inventory, your deduction can be denied if you are audited. (And if the condition is poor, you can't claim any deduction unless you have a signed appraisal from a qualified appraiser.)
The fair market value is what a fair buyer would pay a fair seller in a free and open sale for the same or similar item in the same condition. You can probably find estimated of fair market value for your items from eBay listing, Facebook Marketplace, or the prices that the thrift store sells the items for.