There are several kinds of rabbit safe litter that you can use, and ones to avoid. You should not use pine or cedar shavings, clay litter, clumping litter or corn cob litter.
Safe litters are:
Paper pulp litter, such as Carefresh (paper crumbles), and Yesterday’s News (compressed paper pellets).
Oat or wheat straw pellets, such as Oxbow Eco Straw and Critter Country.
Compressed pine pellets, such as Feline Pine.
Aspen bark shavings or compressed pellets, such as Aspen Supreme.
Straw or hay.
Shredded newspaper.
Horse stall pellets, such as Equine Pine.
Wood stove pellets (plain, with no accellerants).
These litters can be found in pet supply stores, home stores, horse supply stores or online at Amazon or various pet supply websites.
For the floor of the cage, you can use fleece blankets, but watch for chewing. You could also use woven grass mats.
It’s usually advised to wait until a rabbit is 12 weeks old before starting with veggies.
Check out the BUNNY INFO link at the top of the page for a lot of helpful information.