Actually, gift cards aren't necessarily a dead end.
Most of the grocery stores within walking distance are small, not big chains that would have gift cards for sale online like Amazon, Walmart, etc. But there's a chance some groceries I need to prepare a meal are available at a local chain store. It's less decentralized, but if nothing better comes along, it could happen.
As for needing physical cards to be mailed, I could rent a local mailbox using cash, at a place that doesn't record ID. Generally it's about $15 a month and then you have a fairly private 2nd address. Drop by with your key and check it once or twice a week.
Email's not a problem. I can get a protonmail account for free, with a fair degree of privacy and decentralization. If you mean somewhere for gift codes to be sent?
No smart device, though, so if the gift "card" has to be done with a specific app that my PC can't run, it won't work for me.
I'd have to check specific companies/sites/services. I'll do some searches this week.