If I am a landlord and my tenant passed away about 30 days ago, what can I legally do with his belongings?

This question would depend on the state that the property is located. Typically if a tenant dies, the landlord must preserve any property of the tenant who has died and provide reasonable access to the rental unit to allow the executor of the estate or family member to remove the tenant's property.  The landlord is permitted to sell, retain for the landlord's own use or dispose of the property once 30 days have passed from the day the tenant died.  Please check your state's laws to confirm.