I think the number one would be art. That would be a really good sentimental gift. Or you could buy commissions, but that may get costly.
Maybe something that represents them. Like a wolf necklace for a wolf fur. Or a stuffed animal that represents them.
My pressies for boyfriend tend to be a mix of hobby-related things (small tools and similar, as he likes to tinker, and maybe some beginner-level art supplies), otter things (his fursona is an otter), tea/tea accessories (he loves tea), random furry stuff, and dumb gimmicky things. One of the most successful gifts last year was actually a thingy from Flying Tiger that was a “magic bean” in a little can of soil. You were supposed to plant the bean in the can for a cute little houseplant.
He has since transplanted it to our indoor window box and it’s got a bean pod very nearly the length of my forearm. XD
I think some of the best fire gifts you can give are ones that intersect with other hobbies/interests/groups the person is part of. I got boyfriend furry pride pins a couple years back, for instance. A furry stamp collector might appreciate some animal stamps. And so on.
I would give away more custom art as gifts, but I barely draw these days.
Anything with their animal on it. You should just SEE the collection of wolf t-shirts, coffee mugs, posters, paintings, sculptures, bedsheets, towels, etc etc etc I've accumulated over the years (and calendars every year, of course), most of which were gifts.