I'm careful with the kitchen scraps I give mine... like the beans, they get those with no added spices are anything. Not actual left overs from the meal itself, but their own ration from before it's altered for humans. Never any left over canned beans. Too many additives and I'm not sure what is harmful and what isn't. Shelled sunflower seeds will fatten them up good too, they're expensive as a treat, so I buy the 5 lb bag and mix it with whatever other goodies I have for them. I haven't fed corn in YEARS besides what is in the layer pellets. But they enjoy corn cob left overs.
Any seed with a shell, like Pumpkin or squash, I grind it whole in the blender and they can grind it down the rest of the way. I just don't feel comfortable giving the whole seed, they seem giant. Small seeds from cantaloupe or cucumber they get whole.
But with my new flock after not having chickens for little while... no illness at all, giant eggs (even my pullet eggs are a decent size) and they're so dang fat I don't have to heat the coop. I have a light on the water to keep it thawed. When I fed only scratch corn and layer pellets, every winter had to deal with the chicken cold, they weren't as fat, and the eggs were average. My babies are started on Game bird feed and special treats. Fastest feather growth I've seen, over all the flocks I've had. Lot's of good differences over the way I used to raise chickens and the way I raise them now. I bought hens in molt and after a week here they'd start laying again. Slow, but eggs none the less. Haven't had a dry spell on eggs at all, always at least 2-3 a day from the 5 old enough to lay. Several times now I've been 5 for 5 a couple days in a row. Flocks before this... I'd be lucky to get 1 egg from 10 girls in December/January, light or no light.
They may burn out faster from all this laying, but I bet I won't find a better stew hen from any store. Supposing I could go through with it, only ever removed mean roosters.