Green plastic shreds - not really food, but unfortunately they always try to snatch them, probably thinking it's a special kind of grass.The stuff keeps flying around in our garden and the run and I always remove any I see but the chickens are just faster...
The metal bars in part of the coop - no idea why they keep pecking at them.
On the slightly more nutritional side - old wheat semolina from the kitchen cupboard that has grown little worms in it - if I mix it with water to make a mash, they go crazy about it.
My fingers if I don't pull them away in time...
Any form of plant life, including bougainvillea, a cactus, thistles...