Devout Buddhists (or is it Shintoists? Japanese blend the Buddhist philosophy and the Shinto ancestor worship into one religious tradition) may put a plate of three oranges or of white or pink rice patties (mochi) on one of the shelves in deference either to gods or ancestor.
We had a tokonoma on the Phoenix, high on the wall of the "ladies' cabin," on the wall just aft of my mother's bunk. It was maybe two feet by three feet and divided by a cherry log perhaps an inch thick. We had a miniature wall hanging made for it before we left Japan. I wish I could remember what else we had in it--I must have looked at it hundreds of times but I can't remember and the tokonoma and everything in it has disappeared. I can't find a single photograph of it, even in the background of a photo of something else but here is a full-sized one from Pinterest.