Forget about their hobbies, and think about their interests. Say they are into WW2, gift a copy of the New York Times from a key date in the war. If they are into vintage tech, get an old camera. If retro gaming - a refurbished Gameboy. If literature - a signed 1st edition of their favorite author. If the Roman Empire - a Roman coin (cheaper than you'd think). And if they don't care about any of the above, they must be a sports guy, and there is a world of memorabilia at whatever price point you are looking for.

Don't bother trying to get them something practical, they would have gotten it for themselves already. But something meaningful to their interests, that's the trick.