What documentation do I need to substantiate charitable contributions?
I was just audited by the NY State, and they're requesting canceled checks AND receipts. However, for some of the contributions, I have a receipt but, for some reason, I can't locate the canceled check. IRS Pub. 526 states that you need either a canceled check OR a receipt (unless it's $250 or more that you need a receipt.).

Does anyone have experience with this issue?

You need to contact your bank for a copy of your canceled check. as irs said, you need either a canceled check OR a receipt; If you ever donate $250 or more at a time, you need a receipt from the organization. If not, your canceled check or other documentation is all you need. For example, if you give a regular weekly donation of $25, you don?t need a receipt as long as you have some kind of record, even though your eventual contribution is far greater than $250.
Please contact NYS for more info if it is OK even if you have only a receipt ; It is up to NYS