Kong are ton of fun (never tried one myself, but prepped many times for our dogs). :hiphip:
You can pack them with pretty much anything (we usually fill with mostly dry dog food, mixing in odds and ends from the fridge like diced carrots, diced apples, lowfat cheese, lowfat cottage cheese, leftover meat, rice, and/or a tiny smoosh of peanut butter). While I personally think it's A-okay to give "people food" to dogs, I'm always careful to choose healthy foods that are low fat ('cause a high fat intake can be very dangerous to dogs).
My goal is a very snug pack that allows a balance of work and reward that keeps them busy for a while.
We have bought many Kongs through the years, and the hardest part for me is matching the dog to the Kong - they come in different sizes and different strengths. Our pit bull needs a large extra-sturdy one, but our similarly-sized rottweiler does best with a medium regular-strength one. Too bad I didn't invest in the Kong company BEFORE I bought a dozen!
Oh, and speaking of Kong investment, one of the few toys that has ever lasted at our house for more than a day is the Kong Cuz. Ooooohhhh, they squeak like a SUNNAFABITCH (the canine equivalent of a drum set on Sunday morning), but are sturdy as can be. There's the good Cuz (no horns) and the bad Cuz (with horns).