Your person needs a letter if the amount is more than $250. The wording I have the charity (in my case, a private foundation) use in their acknowledgement letter is:
"The Foundation hereby acknowledges you have incurred the following reasonable expenses on behalf of the Foundation, and have waived your right to seek reimbursement for these expenses under Section 8 of the Foundation's Trust Agreement. These amounts may be deducted by you as additional charitable contributions:" 

The letter also includes a detailed listing of dollar amounts, dates, payees, and a narrative description of the expense.

And, of course, "No goods or services were provided by the Foundation in return for your contributions."