Pogue is pejorative military slang for non-combat, staff, and other rear-echelon or support units. "Pogue" frequently applies to those who do not have to undergo the risk and stresses of combat as the infantry does.
"POG" is a backronym for "pogue," raising to prominence during the Global War on Terror (GWOT). The form "pogue" can be found in pre-GWOT novels and books written about the Vietnam War, including in glossary entries which give no indication that the term is an acronym (c.f. The 13th Valley by Vietnam veteran John M. DelVeccio).
The term is said to have been used in the United States Navy and Marine Corps since before World War II, but it did not enter Army or Air Force terminology until some time after the Vietnam War.
Due to having lost contact with its linguistic source, the modern military vernacular has turned "pogue" into a retronym/backronym, e.g., Personnel Other than Grunts, or Person Of Greater Use Elsewhere, the latter referring to mid-grade and senior military personnel who may have been trained/qualified/experienced as combat specialists (e.g., infantry, armor, special operations forces, fighter and bomber pilots, etc.), but who have been assigned to rear echelon staffs, especially senior command staffs.
"Pogey bait" is a reference to sweets or candy, which was in usage in the military as early as 1918. The term alludes to food (and other luxuries) rarely afforded to grunts in the field. To an infantry soldier, the term "pogey bait", when used, in the possessive sense (i.e. "my pogey bait", "his pogey bait", etc.) refers to a personally acquired (not issued) stash of snacks and food. Common items found in a bag of pogey bait include Ramen Noodles, hard candies (i.e. Werther's Originals, Jolly Ranchers, Dum Dums, etc.), Beef Jerky, Easy Cheese, and Vienna Sausages (among other things). Pogey bait was/is used "in the field" not only as snacks and meal supplements, but also for bartering (commonly either for other food or for tobacco products).
In early twentieth century gay culture, the term was an insult: "pogue" was slang for a young male who would submit to homosexual advances.