You can litter train a rabbit pretty easily, thus there is no need to fill a cage with bedding. You want to avoid cedar with rabbits as well. The best is to use some sort of compressed paper bedding, or wood stove pellets. Put some hay over the litter in the box, makes it more inviting to sit, eat, and go potty.
I use a puppy excercise pen as a cage for my heffer rabbit-
