Of all the toys we have bought for our cats, a cardboard box is their favorite.
Always one in the kitchen, when they finally rip it up, just replace it with another.
We get drinking water by the gallon jugs, it comes in a 6 gallon container cardboard box, the boxes never get thrown away.
New cheap toy every week, LOL.
You got THAT right! We must have hundreds of $$ worth of crinkly tunnels, whirligigs, balls with feathers, balls with dingle bells, soft balls, hard plastic balls, big stuffed mice, small stuffed mice, squeaky mice, catnip furry rats, you name it, and after a few minutes it's ho hum, what else you got?! But ANY new box, or large paper bag, by simply throwing it on the floor, can occupy them for days. They invent all kinds of games and uses for them. How we DO indulge our babies.
Large take-out bags, like from Outback, that have handles to them, we discovered we have to cuts the handles or else they get them around their necks and race off with the bag following. It gets pretty funny but we don't want them to attempt that when we aren't around to free them. Our Stella had the habit of sticking her head in a square kleenex box and then racing around bumping into the walls she can't see! Sometimes they pay for themselves in entertainment value alone. ;o)