"Down to the shirt on his back"
It's a German saying that means 'to give your last possessions' . The English phrase has basically the same meaning. I guess many Germans will have the image of the girl in the fairy tale "Sterntaler" (The Star Money / The Star Talers) in mind when they use the phrase. http://www.pitt.edu/~dash/grimm153.html
Translating one idiom into another idiom doesn't feel like the most effective way to teach things...