In the bag

In the bag means that something or other is a virtual certainty and is of American origin from the late 19th/early 20th century. It is a metaphor for something being secured i.e. literally in a bag and of all the explanations of its origin, and there are many, the most plausible is the simplest, namely that it derives from shooting birds and small game, which were put in the bag. See also Bag/ baggies/bags/bags of