Yes.
See this IRS web site https://www.irs.gov/government-entities/federal-state-local-governments/de-minimis-fringe-benefits, which says, in part:
"Cash or cash equivalent items provided by the employer are never excludable from income. An exception applies for occasional meal money or transportation fare to allow an employee to work beyond normal hours. Gift certificates that are redeemable for general merchandise or have a cash equivalent value are not de minimis benefits and are taxable.
A certificate that allows an employee to receive a specific item of personal property that is minimal in value, provided infrequently, and is administratively impractical to account for, may be excludable as a de minimis benefit, depending on facts and circumstances."
There is no exception for non profit employers. Although the the donated items have no wholesale cost to the employer, they still have a retail cash value.
From a practical standpoint it depends on why you are asking. If you are questioning your employer including the amount on your W-2, yes they can and should do that. If they did not do that and you are asking whether you should include it as income, the answer is yes you should; but "nobody does it".
Here's another article on the subject https://www.shrm.org/ResourcesAndTools/hr-topics/compensation/Pages/Holiday-Gifts-Taxable.aspx
