nothing to really add to the wet food thing, except cottage cheese...
for the kong, try putting just a little bit of different things in it for a few days, clover always "liked" his kong, but wasn't really into it at first, ie-he didn't "love" it... now he waits for it every morning in his crate... i really like having something i can give him when i leave that i don't feel he needs supervision for... so far it is the only toy that he hasn't shredded...
i mostly use peanut butter and cream cheese bc they are cheap, but you can also use canned dog food (or salmon

) basically anything that you can "smear" that is safe for dogs to eat. clover doesn't like canned pumpkin on it's own, but i know other dogs that do... or mushed bananas, baby food, you can also try putting stuff in and freezing it....