Another common object I've found that all of my cats have liked to play with has been just an ordinary box regardless of whether it's empty or has something in it. Much like this cat:
Or maybe a box designed by their owner like this one:
However, the poor cat doesn't really look too happy since it probably wasn't his idea. Just plain old boxes will do. My younger cat, Sammy, likes to tip over the recycling box that we have for papers anytime it's empty. Once papers are in it, he leaves it alone. But, if it's empty, he can't resist!
They can keep themselves entertained very well just as Kirby did with my swimming suit strap. Or like these cats:
From catching butterflies, to exploring:
to being hyperactive:
Get two kitty cats together, and they can come up with most anything!
Sometimes their play will get them into very awkward places.
But, however they play, you can be assured that you will be laughing and thoroughly entertained!