Good links...(wait for it)..........but.... the websites don't give clear enough warnings on the amounts of say, peanut butter, you can put in a Kong - pack a giant Kong with peanut butter and chucking it to Fido is going to make him a roly poly doggy in next to no time! I'm not too hot on the idea of yoghurt & cottage cheese for dogs either, it is my understanding that dogs are cows milk intolerant due to a dogs inability to produce lactase.
Things I've put into Kong - Billy & Margot do a non dairy doggy ice cream which is great in summer - there are other frozen yoghurts available for dogs but I haven't tried them. We have mashed up their dry dog food with water and added whole kibbles and then packed them into a Kong. Another one is to smear doggy pate around the inside of the Kong and the dog keeps licking long after the pate is gone probably because they can still smell it.