Are we talking about the most important possession, action or belief?
My most important possession is a vehicle. It gets me where I need to go and in a pinch I could live in it.
My most important action is to analyze and comprehend. When I understand a situation better I can choose my other actions better.
My most important belief is that God is still in charge and actively working in this world. True faith is not believing God will give me what I want, but believing God still loves me enough to take an active part in my life even when I don't get what I want.