Onions are bad for chickens and other animals, so I would not give those. The best thing you can feed them is a good balanced layer or all flock (Flock Raiser) feed. It has all of the protein, vitamins, and minerals they need. Do you have some crushed oyster shell available for calcium and hard eggs shells? They will always chose scratch grains or corn, since they taste like candy, but it doesn’t have but half the protein and few nutrients to offer. It costs a few dollars more, but you will probably use less in the long run.