Generally, rabbits have no need of bedding in their area and only require a soft surface to lie on. You may want to invest in a softer surface if the bunny mostly resides on hardwood flooring, slippery surfaces, or rough carpet. See Housing#Enclosure Setup for more details.
Common flooring used in rabbit housing enclosures are towels, blankets, and rugs. Some people also use CareFresh as bedding in a rabbit's cage. For outdoor hutches, straw is a great insulator in the winter and allows rabbits to dig and nest in it. You may also use more expensive regular hay.