Why does the food supply in the hiding place diminish toward the end of the play?
I'm not sure, I've never seen the play. But I know in real life, it diminished in part due to many thefts (mostly done by the warehouse worker), and because Germany was in a recession/depression again (I think recession is too light a word for what it was and a depression too hard. I think it was somewhere in the middle of those two, but I'm not 100% certain).
I also know the person that supplied food got arrested. If I recall correct, there was a second person, but I'm not sure if the second person ever got arrested, or if the first person ever came back.