Anything free is better, sex with 2 women or more is better. However as to your inquiry of what to put in the tank with dragons, rocks, sand (calci-sand), and maybe some wood. Dragons come from more desert regions with few plants.
it comes is 4 differnet colors and is very sanitary, you should get afew, so during maintanence you can throw the soiled ones in the washing machine and have new ones ready to go
also you could have soem big rocks and some grape vine for climbing and basking