My understanding is not to give your chickens milk or milk products (with the exception of yogurt) because they can't digest it well. Yogurt has probiotics that help the chickens with digestion, etc. Bananas are great, and I want to know what Weetabix is. Is it like a cereal? If so, I'm sure it is fine in moderation. If your chickens free range, they likely get everything they need during the day.