We held a fundraising auction. Can I issue charitable donation receipts for the donated auction items?

It depends what the items were.

You can issue tax receipts for gifts of property. Thus, the donors of tangible auction items – artwork, an iPad, a bicycle, anything you can touch – can receive a tax receipt for their gift.

You cannot issue tax receipts for gifts of services (e.g. a tax consultation, a spa treatment) or for promises of services (e.g. a gift certificate, a voucher for hotel accommodation).

One important point of clarification: the company that issues its gift certificate or the hotel that issues the accommodation voucher has given you only a promise; they have not transferred property. However, if someone other than the issuer purchases a gift certificate or voucher (i.e. pays for it with cash) and then donates it to you, they have acquired property and made a gift of that property – and in that circumstance, a tax receipt can be issued.

Here’s the citation from the CRA website.