(slang) Certain or extremely likely to occur.
3-0 up with 5 minutes to go...we've got the win in the bag.
(slang) Intoxicated.
Source: en.wiktionary.orgI was teased if I brought my books home. I would take a paper bag to the library and put the books in the bag and bring them home. Not that I was that concerned about them teasing me - because I would hit them in a heartbeat. But I felt a little ashamed, having books. Walter Dean Myers
I have a bag full of words, and when one of us comes up with a good piece of music, I look in the bag to see if anything there will fit. If nothing does, I sit down and try to put down on paper what the music makes me feel; very rarely will a piece of writing inspire a piece of music. Robert Smith (musician)
We won't say four, till we have them in the bag. Antonio Simeone Sografi
To buy the pig in the bag. Swedish Proverb
Problems are in the bag. Corsican Proverb
Don't say "wheat" until it's in the bag and well tied up. Catalan Proverb