I've used so many things in the kongs. You seal the small end with peanut butter so nothing will leak out while it freezes
Some of the favorites are canned food, organic low fat plain yogurt, kibble, freeze dried liver treats, honest kitchen, grandma lucy's, chicken baby food, frozen green beans, pumpkin, and I just got this stuff for them called Noshers (
Pet Fairy Noshers - Fancy Fillings<br>(great with Kong toys!) and other Pet Fairy Noshers - Fancy Fillings pet products on sale at DoggieFood.com) that I am going to try this weekend when I fill Kongs. I normally pick a filling (yogurt, grandma lucy's etc), then add something else to it (treats, kibble, green beans, etc). They don't get very much of any one thing, and don't get them every night, so their weights are fine.