If your shower stall has no shelves built-into the wall, you will probably need some kind of stand-alone shelving unit to hold your shampoos, conditioners, creams, sponges and whatever else you like to use. Of course, you will want something that will not rust or rot, so you may want to opt for something that is made especially for showers, rather than any old shelving unit.
Here are two examples – I don’t really like the curves of the model on the right, but I do like the fact that it’s made of wood:
Free-standing shower shelves pictured:
Left: Three Shelf Corner Caddy in Chrome Plate by Organize It All
Right: Freestanding Teak Curved Corner Shower Shelf with Pull Out Soap Dish by Signature Hardware