Yum! Screw boxes are a favorite. Especially when you forget to bring one in and they get soggy. Earplugs are hit too. I chased down a few hens for taking them. I don't think they ever swallowed one.
Before I lost too many birds, mine free ranged. I caught them eating or trying to eat about everything. Foam, cardboard, paper. They about pecked their way into a tube of caulk I had set down while I was working.