If by chance you have metal shelving, and items fall through them, you can cut pieces of cardboard to the size of the shelf and place them on the shelf. That way nothing can slip through the slots made by the metal shelves.
If you can’t find one piece of cardboard that is large enough, then you can use heavy-duty packaging tape to tape however many pieces of cardboard together that you need. I had to do this in my bathroom and in my bedroom. I also found it necessary to put pieces of cardboard on my laundry shelves.
They were placed at the back of the shelves, right up against the wall, so that my washcloths and small folded towels wouldn’t fall off of the shelves and get behind them where I wouldn’t be able to reach them. I learned this by having to move out the shelf unit that I had put them on, and retrieve some of the washcloths.
Needless to say, I only did this once before I got smart and put the cardboard to the back of all of the shelves on the unit. I wasn’t going to take any chances on having to move that shelf out again.