You should keep all of the receipts related to your rental as proof of expenses should the IRS ask for them. You can choose not to deduct any expenses that you don't have a receipt for (or a cancelled check, money order and/or credit card transaction). Or... you can choose to include those expenses, but be aware that the IRS may disallow them later. Any disallowance could result in interest and/or penalties should you be required to pay anything back.