in the bag

used to convey that something is guaranteed to be accomplished

The origin of the idiom "in the bag" is actually uncertain, but there are a few theories about its origins. One theory is that it comes from the world of hunting, where a hunter who successfully shoots and kills an animal would place it in a bag to carry it home, implying a successful hunt. Another theory is that the idiom comes from the sport of horseshoes, where a horseshoe that lands in the scoring area is "in the bag" and scores points for the player, indicating definite success. The idiom is used more generally to describe a situation where achieving success or victory is considered certain or very likely.