Just be careful not to let the cat out of the bag, or someone may leave you holding the bag.

VOA: special.2009.01.25

If you tell about something that was supposed to be a secret, we say you let the cat out of the bag.

VOA: special.2009.09.27

The phrase to be left holding the bag is as widely used as the expression to let the cat out of the bag.

VOA: special.2009.01.25

Some of the oil will flow out of the bag and can be collected.

VOA: special.2009.09.29

Another widely-used expression is to let the cat out of the bag.

VOA: special.2011.05.22