Make sure to sterilize anything you bring in from outside sources before putting it in with your snake!
For wood and bark: Easiest way is to scrub it really well with soap and water, then drop it on a cooking sheet in the oven for a few hours at 200 degrees. Do Not Leave It Alone. It can still be a fire hazard of left unattended.
Do not cook rocks cause they can explode. You want to soak them in bleach for 24 hours, then rinse them fully before letting them dry completely.
But that will kill off any bugs or bacteria lurking on there.