I keep all the trimmings from roasts or other meats, cooked or uncooked, I freeze them as they accumulate. All the shells from shrimp or other seafoods. And anything else, such as the tough stem parts of cauliflower, broccoli, or asparagus, extra or gone moldy squash, pumpkins, beets, cooked beans, peas- ANYTHING that came from food good enough for us to eat.
When I'm away from the coop for more than a day or so, any eggs found on return go into the "recycle" bin too.
When I've got enough of such scraps saved up, it's chicken feeding time! The meat scraps all come out of the freezer, get cooked long enough to sterilize/soften and the whole batch gets put into the blender, eggs with shells and all. Whipped and chopped in the blender, pour it into a ceramic "meat loaf" type pan, microwave it into a big, oddly colored soufflé!
THE CHICKENS GO NUTS FOR THIS! And boy, do the eggs have nice dark yolks afterwards. Only drawback, the chickens who've eaten such a high protein supplement do have rather manky poo for a day or two after-
PS- Went to an outdoor wedding on a farm Saturday, look who they had for ushers!