I understand that you, and only you, knows best what you desire and that the best I can do to help you is to give you the most universally desired means of exchange.
Gift cards are a ripoff and if you give them you are (normally) doing a disservice.
(FWIW, I actually agree with you, and I imagine there are a lot of others. The hardest part is interacting with those who don't view rationality as an appropriate filter for a celebration, especially celebrating things like 'your not dying in the time it took for the earth to complete a full rotation of the sun', or 'a family-centric federal holiday to mark an apocryphal historical event that has developed societal importance'.)
Perhaps, encase the cash in something that, while not very expensive, required a lot of advance thought/planning?
For example: the enclosure-with-cash needed to be ordered long in advance. And also, encased inside with the cash is some dated and/or custom artifact, such as a personalized note or recommendations of things to buy.
Overall, it sends the message: I rationally want you to buy what you want, but I didn't just thoughtlessly drop a bill in an envelope at the last minute. I've been thinking of you on this gift-giving occasion for a while.