What an great answer to the question. Yes- look to the interests of the kids, but you have to work with them a year or two to figure that out. One thing I would make an exception to- last year I brought in my racing bicycle and my sons bicycle and the 5th graders had the chance to draw from these, then later I had them take the best 6x9 inch section and then sharpie and water color that and they loved it. My kids did love the bicycles and the paintings by Taliah Lempert. Otherwise I agree, we have limited space, fill it with their interests once you figure them out.
They don't care about drawing bottles and bicycles, etc. Have them bring in what they want to draw for a still life and then get rid of it.