What is the ruling on placing certain objects on top of religious books or placing some religious books on top of others?

There is no harm in placing religious books one on top of another, but they should not be placed on top of the Mushaf (copy of the Qur'an), which should always be higher than all other books. It is disliked to place cultural books or other items on top of religious books, out of respect for the ذكر الله (remembrance of Allah) and knowledge of Sharia contained within them. The ruling may even reach prohibition if it involves disrespect or insult.