Q: Can I give my chickens moldy bread, moldy leftovers or moldy feed?
A: No, your chickens should not eat anything with mold on it. Just as moldy or rotten food can make you sick, it can make them sick. Sharing some leftovers you don't want with your chickens is a good idea (in moderation). We often give our chickens leftovers there aren't enough of to bother keeping... but they must not be moldy or rotting . Stale bread can be okay, although it probably won't have it's full nutritional value... but mold? No. Certain types of mold can be quite dangerous. The same goes for their regular chicken feed: if you see mold, simply discard it. And as for any leftovers that have actually gone bad or started to rot ? There's a reason we say food has "gone bad." It's BAD. Chickens can get food poisoning, too. Discard such food.
And here's a final tip: when getting baby chicks, some people like to get everything early, including food. It's a great idea, in fact! Be prepared, as the scouts say. You don't want to receive baby chicks and then have to scramble to find the proper food at the last minute, right? So many people get their chick food early and keep it in the freezer to prevent it from getting stale or buggy. (Stale or buggy food won't hurt them per se---they eat bugs after all!---but it has lost some of its nutritional value.) The freezer does a good job of keeping it fresh. However, when you take it out of the freezer and leave it at room temperature, perhaps by your brooder sealed up in a container, be aware that condensation on the icy food can then lead to mold growing on the feed. So you'll have prevented one problem only to cause a worse one!
So, DO get your feed early... but DON'T get it months early. And if for some reason you do get it way early anyway, then leave the bag open (in a non-buggy spot indoors, if you please) for 24 hours or so. Before you seal the bag or your feed storage container, run your hand through to see if you can detect any moisture. Then keep a sharp eye out for mold, just to make extra sure your chickens will be eating healthy food.