It helps me to recall that, for a non-cash gift, the acknowledgment is supposed to describe the property received in sufficient detail to identify what was received. So, one share of IBM common stock is exactly like another, so "1 share of IBM common stock" is a sufficient description, but it's different for, say, a work of art, which is very likely unique (Edvard Munch painted like 3 versions of The Scream!).
So, with that in mind, your acknowledgment of the gift card should identify it in sufficient detail to identify it, and a gift card with a face value of $100 is different from a gift card with a face value of $5! You aren't stating a value, you're describing the property.
As John indicates, just as gifts of services or of a partial interest aren't deductible as charitable contributions for federal income tax purposes, gift cards redeemable for services or for a partial interest in property (like a hotel stay) aren't deductible either, and I wouldn't generally acknowledge those in a way that resembles the acknowledgement of a deductible gift (no IRS language, etc.).
That does highlight another aspect of the description of the gift cards, namely, specifying what the gift card can be redeemed for, e.g. "a gift card, redeemable for merchandise at the Smithsonian American Art Museum Store, with a face value of $50." Similarly for gift cards for specific items, e.g. " a gift certificate redeemable for the exhibit publication The Shape of Power: Stories of Race and American Sculpture at the Smithsonian American Art Museum Store."
(It gets trickier if the gift card could be redeemed for either goods or services; the best way to handle that is to work with the donor so that the gift card is for the one or the other.)
My US$0.02 worth; the usual disclaimers apply.
Thanks,
Alan
Alan S. Hejnal (he/him)
Data Quality Manager
Smithsonian Institution - Office of Advancement
(: 202-633-8754 | *: HejnalA@si.edu