I assume you are referring to a Charitable Deduction?
Yes, you can deduct your ACTUAL expenses, but you can't use the Per Diem amounts.
You can NOT use the standard Lodging amounts; you can only use your actual cost for Lodging. As for meals, I have never read anything that allows the meal Per Diem for charitable work. Assuming that no provision exists for that, only your actual expenses can be used as a charitable deduction.
