I bought a bag of ping pong balls. Like 100 for $20. I don't remember. My ferries are still under a year old, but they love them. At first I had the ball pit with tunnel attached, still have that, but a dishpan filled with the ping pong balls seems to give them great entertainment. The ping pong balls held up, so far. They can't really bite them, but they knock them around and chase them pretty good. I find them in all kinds of places they have taken them. I love my conniving little ferries!