I always try to avoid processed foods wherever possible. So I make a mixture of whole barley, whole wheat, and whole oats. They also get a daily serving of kitchen scraps that we gather from friends.
I do sell the eggs when we have extra, but mostly we raised them for our own consumption.
Our ducks are about the closest things that we have to "pets" on the farm. With our limited space, every single animal has a purpose, preferably multiple. But we got Muscovy ducks for my little brothers many years ago (see the pictures below, quickly, before they Indian-burn me until I take them down) and we just loved having them around... So since they eat slugs and mosquito larvae, and free-range successfully without us having to feed them, I got some again!
We let them do their own thing entirely, so we end up with ducklings over the summer as well, which is so much fun. We sold several of them, kept one hen, and will be putting the last 3 drakes in the freezer (Muscovy are renowned meat birds) so we don't over-populate the farm.
Each morning they get some bread with the pigs and chickens, so they stay tame and friendly, while costing us practically nothing.
Like the free-range chickens, they get into boxes of scraps and poop in irritating places, but they're about the cutest, funniest things you'll ever see... Watching them stealing food right out of the pigs' mouths, and pecking them on the nose if they resist, has me in stitches on a regular basis.