Headlamp: A deer hunter can never have too many headlamps because they go missing all the time, either lost in the bottom of a daypack or dropped on the way to or from a stand. Spend $15 to $100 for a lamp, a wide range of them is available.
Gloves: A good pair of leather shooting gloves, or a waterproof camo set makes the perfect stocking stuffer. One of the best gifts I ever got was a pair make out of the tanned hide of a buck I shot. My wife saved the hide and sent it off to a tannery/leather maker.
Shooting Glasses: A good pair of clear or amber shooting glasses for sighting-in.
Earmuffs: A bag of orange foam ear plugs is great, handy and cheap.
Stocking cap: Stuff a camo or blaze-orange skull cap into a stocking.
Multi-tool: I don’t know any outdoorsman who wouldn’t love a new Leatherman or Gerber tool.
Knife: Any hunter will appreciate the quintessential stuffer, whether it’s a fixed-blade or folder. But no cheapies, gift a quality knife like a Case or Buck.