Oh gosh...

Yes, but not everything is good for them

i never said it was

And bugs, grain, plus each other and eggs if allowed to.

Not in most places they're farmed. If you're farming a lot at once, then they're usually grain fed.

They don't eat grass like a cow would, they browse on the seeds and grain produced by the grasses around. And whospikedthepunch is correct, they eat insects and other meat (including chicken meat).