My cats' favorite toy is a foam earplug. My husband works construction, they fall out of every pocket when we do laundry, the cat will play with an earplug for days! I agree with the paper bags and cardboard boxes. Every bag and box goes to the cats until recycling day. You could make a sock ball that they are allowed to have. Anything they are allowed to climb on is fun, find something you can stack and then stack in a different way. I found both my cats in a standoff around the laundry basket last night, any sort of basket is fun. Catnip is easy to grow in a small pot indoors. If you have some rope/twine you can wrap a railing post to be an acceptable scratching spot. You can make a ball out of tinfoil.