I would love to hear what other people stuff their dog's kongs with;  In Summer I freeze the contents (sometimes meaty stew or stock or just bits of meat, veggies and peanut butter with water added to stick it all together).  Other times I stuff them with whole dog biscuit shapes (Lucky Dog bones, minis etc.), cheese bits, dry dog food and even fresh chicken necks and wings (hard but possible!).  I love the idea I just read in 'Boredem Busters' about soaking the dry food in the kong, so it expands.  Looking forward to trying that, and can't wait to here other suggestions!