Like Hilde said, mine love me to make forts out of cardboard. Cut a hole in one end of a large carboard box and they will have tons of fun going in and out, making new holes, and making the hole you made bigger. Mine get boxes left over from everything. Cat food boxes, ice cream sandwiches box, and breakfast bar box. They will chew those smaller boxes and throw them around.
As Hilde does, I also offer mine old phone books. Mine love to just rip the pages off.
You can fill the toliet paper rolls with hay. I hang some from the cage bars. I also use paper towel rolls for different sizes.
Just to change things up, I will take toys that are laying around their cage and attach them to the cage. All the sudden they will find a new interest in that toy. I have also cut pieces of cardboard and attached them to the sides of the cage.
I just want to say, make sure if you offer boxes and paper. You make sure the bunny doesn't ingest a lot of it. Mine tear it up and leave piles on the floor.