Of all the low hassle animals in the world, chickens are the top. They eat the leftovers. They make eggs. No food is wasted in our house, ever. My kids are free to never clean their plate, because we have chickens.
Also, still worth it, mini-goats. No, we don’t milk them, but they’re so darn useful! No mowing. No smell. No biting. Eat all kinds of vegetable-end leftovers the chickens would ignore. All we do is make sure they have water. That’s it.
Also still worth it. Perennial herbs. Mostly because they haven’t died in the face of serious neglect, and my daughter likes to make fresh hot tea all the time.