Every cat's favorite, the milk jug rings.
Tomas loves the large furry mice, the 3-4 inch long ones. The plastic eyes and nose could come out easily so I pull them out with a pair of nail clippers. The smaller mice are dangerous, I had to pull one out of a cat's throat years ago.
A furry ball thing with eight 'legs' on it, sort of looks like a weird octopus.
Mini tennis balls made for small dogs and normal tennis ball.
The plastic practice golf balls with the holes in them, heavier than a ping pong ball and a bit larger.
Leftover arms, legs, and bodies from messed up sewing projects.
Homemade yarn pompoms. If well made they can even be tossed in the washing machine, as I found out when Sho used to leave them in the dirty laundry hamper. I haven't made any new ones since Tomas shredded the others.
And a small stuffed snake toy that both cats love carrying around.
I won't buy anything that could break or choke them.