You will report the total sales as Income as your Schedule C.  You will also be able to deduct the cost of the items on that same Schedule C.  You should be keeping records of the purchases of the items.  IRS has no way to determine the cost of the items.  If you have a "best guess" of the purchase price, then use that.  If you were to be audited, you would have to let IRS know that you did not keep the receipts but used your best estimate as the purchase price.  I definitely recommend keeping track in the future!  I'm sure there is an app for your phone that you could use literally at the time you buy the item so it wouldn't be such a daunting task.