I use bamboo in mine. Make sure that it is natural, and not coated in some kind of lacquer like most decorative types are.
As hermies4ever earlier posted in another thread, REAL BAMBOO is fine, lucky bamboo is NOT. Lucky bamboo is not real bamboo and is toxic. Lucky bamboo is that bamboo you see in stores, cheap, with green leaves and NOT hollow. look up pictures of the differences before buying bamboo, so you know what you're getting. =]