I found a useful University of Minnesota Extension guide that explains the basics of how to feed chicken appropriately as they grow.
The guide focuses on complete poultry feed as the nutritional foundation, which makes sense to me because treats should not replace a properly balanced ration.
For my own flock, I would keep extras limited and make sure the birds still eat enough of their regular feed each day.
I would also be cautious with any food that is spoiled, moldy, heavily salted, or difficult to identify as safe for poultry.
Another point I would watch is whether treats are causing the chickens to ignore their main feed.
If that happened, I would reduce the extras and return to a simpler routine based mostly on complete feed.
Fresh water should remain available at all times regardless of what else the birds are given.
For me, the safest approach would be to treat scraps and snacks as occasional additions rather than a major part of the chickens' daily diet.