in the bag

Assured of success, virtually accomplished or won. For example, The coach thought the trophy was in the bag, or Our new contract is in the bag. The precise allusion in this idiom is unknown. One writer believes it refers to a completed transaction, that is, an item bought and wrapped in a bag. However, it may well refer to the game bag in which hunters place small game such as birds. [c. 1920] Also see under wrap up.