Food: Wellness Core Grain Free Small Breed (Bella appreciates the small kibble size since she had a few teeth removed). Royal Canin for Yorkshire Terrier is also good.
Treats: Thawed frozen peas, small pieces of peeled apple, cherry tomatoes cut in half (if you don't precut them, they can make a mess), small pieces of lean ham. For store-bought treats, Bella likes Pet Botanics mini training rewards. I think a Kong is a device that you put treats in and the Yorkie plays with it to get the treat out (see
https://www.kongcompany.com/).