What a great question!
There is a small rock that I can hold comfortably in my hand. I found it at the entrance to a local cemetery while taking a walk. I painted it with some specific words and symbols that say exactly what I and my life are about. It’s not something I show to people, nor would I likely explain the meaning if I did.
But M knows. All of it. I showed him and he held it for a while, so now it’s a transitional object too. By the time I showed it to him he already knew what it meant so very little explanation was needed.
I often hold it during our sessions and it helps a lot with nervous fidgeting that often happens at that time.