You should keep records of your cash and non-cash contributions to support the amount you deduct. There are specific requirements for supporting documentation, generally depending on the amount of the contribution.
Cash Contributions
If you made cash donations, you should keep canceled checks, receipts, or other reliable written records showing the name of the organization and the date and amount given. As mentioned above, if you make a payment of more than $75, that is partly a donation and partly for goods or services, the organization should send you a statement indicating the value of the benefits you received.
If you make a contribution of $250 or more, you need a written acknowledgement from the charitable organization, or payroll deduction records, if the contribution was deducted from your pay.
Noncash Contributions
If you gave property, you should keep a receipt or written statement from the organization you gave the property to, or a reliable written record, that shows the organization's name and address, the date and location of the gift, and a description of the property. For each gift of property, you should also keep reliable written records that include:
How you figured the property's value at the time you gave it. If the value was determined by an appraisal, keep a signed copy of the appraisal.
The cost or other basis of the property, if you must reduce it by any ordinary income or capital gain that would have resulted if the property had been sold at its fair market value.
How you figured your deduction for gifts of capital gain property.
Any conditions attached to the gift.
Expenses
You should keep records of your actual expenses or a log of your mileage, if you are deducting expenses for the use of your personal vehicle in performing volunteer services. You should note the name of the organization, the date, and your actual expenses or mileage.
If you have other out-of-pocket expenses related to your work, including travel expenses, you should keep receipts and evidence of payment, and should get an acknowledgement of your services from the qualified organization.