If you are not receiving a salary, there is no procedure in the tax law to claim a "home office" charity donation. You also can't claim a deduction for the use of any property that own and continue to own. You can claim a deduction for any supplies that you buy that are used for charity purposes (ink, paper, stamps, etc.) But you can't claim for the use of a printer, or the use of furniture, unless the charity actually takes permanent ownership of the donated property.
For donations of goods like office supplies, you would need a letter from the organization acknowledging the donation (but usually not providing a specific value), combined with your receipts (which do prove the value). Since you are the director, you would want to get the letter signed by someone else in authority who can attest to the donation, so that it does not look like self-dealing to the IRS.
