I don't know if I'm particularly mean but I don't really build variety as such into Morgan's meals. He gets a complete food twice a day for his meals and that's more or less it. He does however get raw chicken wings instead of his usual supper a couple of times a week but that's to help keep his teeth and anal glands in good working order
I think variety is more a human concept! He gets treats of raw carrot, broccoli stalks, fish4dogs sea jerky and he gets a bedtime biscuit too, either homemade or James Wellbeloved Crackerjacks. A Nylabone is a good idea for chewing on, they do puppy ones which are not too hard for their little teeth.
In kongs we use peanut butter, bits of chicken or ham, or broken bits of biscuit held in place with cottage cheese or light cream cheese, you can put yoghurt in and freeze it. If you do a search on here for kongs you should get a few more ideas.