Tons of stuff!!! Change it all the time. Your imagination is the only limit!I suggest making it comfortable for you first and in front of the TV or have a good book(you end up staying in a lot longer).
I tried taking toys in there but they also mainly love jumping from my head to my boyfriends head or hanging upside down from the top. I do want to get a feather cat toy thing. I have a hammock hung in there for them. But that's about it.