It's in the Bag

It's in the bag, means that it is a sure thing, a done deal, a slam dunk. The origin of this expression is most likely a hunting reference, in which the prey has been killed or bagged. Many states have hunting bag limits, such as how many deer, moose or bear you are permitted to bag per season. Brown bagging it, usually means carrying your lunch to work or school.

A related bag expression is, "The cat is out of the bag," meaning someone has revealed a secret, or gossiped widely about a secret.