That's a "bird hook". Used to pull the guts out of game birds to prevent spoilage. I was always taught to gut em quick in the field and that hook helps yank 'em out. Great pic of some cool items...that lighter is really neat too.
Thank you all, for the kind words - FWIW, the knife's a late-issue (1980's) Remington that also sports a choke tube wrench in the end opposite the business end; and the lighter's a "Marlboro", from the late 60's.