If you don't eat more you'll soon be a bag of bones.

你要再不多吃些，真的要变得骨瘦如柴了。

youdao

If you don't eat more, you'll soon be a bag of bones.

你再不多吃一些，你将骨瘦如柴。

youdao

I wanted it to be a surprise, but my sister let the cat out of the bag.

我想给大家来个惊奇，可我妹妹却先说漏了嘴。

《牛津词典》

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

For those of you who are on the run from the FBI, your Visa has run out, or you're sitting next to your ex-girlfriend, now would be a good time to put a paper bag over your head.

被FBI通缉的,签证失效的,还有前女友就坐在旁边的,赶快找个纸袋子把脸给蒙上

耶鲁公开课 - 博弈论课程节选

Software can be added to identify things that are not usually there, like a bag left on a bench.

VOA: standard.2010.04.01

It might as well be a bag of flour.

FORBES: Are You Trying to Eat Better?

If you went to a fast food restaurant and purchased a packet of fries and a burger then the fries can be placed in a free bag as they are only part wrapped and you would not be expected to place these in a reusable bag as there could be some food safety risks.

BBC: Quiz: When do you have pay for a carrier bag in Wales?

But the results would surely be a mixed bag: some good, some useless and some terrible.

FORBES: State Health Care Flexibility: The Good, the Bad and the Broke