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Look for bedding that's designed specifically for rabbit habitats, or mentions that its safe for rabbits. One of the best all-around materials available is hay, which is edible and will keep your rabbits warm during colder nights. Pregnant females and babies should be given Alfalfa hay, while fully-grown rabbits can have Timothy hay. Another option is to use a dust-free bedding made from recycled wood or paper. Avoid using pine or cedar chips or shavings, as these can be toxic to rabbits. Put down 23 inches (5.17.6cm) of bedding at a minimum, making sure it's evenly distributed from corner to corner. If you're using hay, mound it around the edges of the cage so that your rabbit can graze while still having an open area near the center for playing and sleeping. For ease of cleanup and extra protection against leaks, consider adding a couple absorbent puppy pads or a layer of newspaper beneath the bedding material. Provide a deep layer of bedding so your rabbit doesn't get sore hocks. This painful condition is extremely common and occurs when rabbits sit on hard, damp surfaces. Deep bedding cushions your pet, lifting them off of soiled spots. While rabbits typically have no problem sleeping on any soft, cushioned surface, a separate bed can make a useful and adorable addition to a well-outfitted cage. Place the bed near one corner or wall so your fluffy friend will have plenty of room to eat, play, and stretch its legs. Bunny beds are available as woven mats, tiny hammocks, and small plush beds similar to the ones dogs like to curl up in. Training your rabbit to use a litter box can help you keep its cage cleaner and more sanitary. Shop around for a small litter box in a size suitable for the species you're keeping and cover the bottom with layer of recyclable paper-based litter. You can also use a mixture of shredded newspaper and hay if you have any extra lying around. Stay away from clumping cat litters. These can be dangerous to rabbits if ingested.

Summary:
Pick up some rabbit-safe bedding. Spread your bedding material along the bottom of the cage. Set aside a place for a bed. Add a litter box.