If you do not know the amounts to use for your Schedule A deductions, it might prevent you from completing Schedule A, but you have the amounts just not the receipts, you can still file. If the IRS questions you and you cannot provide the supporting documents to back up your deductions, they will disallow the deductions and you will have to pay the additional tax, plus penalties and interest.
You do not need to attach receipts for your Schedule A deductions to your tax return. Your receipts and documents are for your records in case the IRS ever questions your deductions.
