It sounds like we’re talking about a “hook” as in what is commonly called a clip, as in a belt clip.
If I have that right, the Specialized Stix headlights have an optional clip that can secure the lamp to straps, webbing, a pocket edge, a shoe upper, waistbelt, or anything thin like that.
They’re awesome little units as marker lights; if you need a light to illuminate a pathway at night, you’ll want something else, and probably a different mounting method since dangling from a clip is not going to allow for aiming and all that bouncing around would get really annoying awfully quickly.
EDIT: Haha…I now see many have noted that bag mounting is a generally poor method; sorry for repeating that. Stix are quite light though, so should be the better performer in that placement than a heavy unit.