Peanut butter, yogurt, blueberries, bananas, canned dog food.
Oh yeah, I also use the Kong stuffing in peanut butter flavor. It's helpful when I'm in a rush and can't prepare the Kong, I just spray the stuffing inside and go!
Or go to the pet store and buy that can of Kong Stuff!
I use wet food and rice, then freeze it. Or peanut butter and freeze it.
Peanut butter then freeze it, also you can use Pattie fillings and freeze it.
dry food, wet food, pb, jelly, anything that is safe for dogs can be put into kong and given at room temp or put in kong and freeze it. the kong wobble is another great toy. has to use dry kibble or treats
I use peanut butter the most; sometimes I put a treat inside, peanut butter, and then I freeze it. I usually only do that if I know I'll be gone for awhile and Frodo needs something to help keep him occupied.
I also fill it up with their own kibble every once in awhile.