How to translate "по коробу поскреби" here.
Короб is a kind of a box, that was used for storing things in old times. Поскреби is a suggestion to 'скрести', which means 'to scrape'. It's like "Scrape the bottom of the barrel", but instead of a barrel it should be some kind of a box.
The meaning here is that the box is empty, but maybe there's something left on it's bottom.