I know you said you were out of peanut butter, But here are a few more ideas to fill the kongs...
Cheerios and peanut butter
Chunks of Apple and peanut butter
Cooked macaroni and melted (not runny) velveeta cheese
Bananas and unsweetened applesauce - freeze
Cream cheese, peanut butter, and applesauce - freeze
Applesauce with chunks of fruit - freeze
Bananas, cooked oatmeal, applesauce, and yogurt - freeze