The sides that do not come with the entree are always extra on the dining plan. You just pay for them seperately at the end like you pay for alcohol (the sides would in fact, be on the check with your alcohol).
At Yachtsman last May, we ordered mushrooms, wine and beer. The Deluxe dining plan covered everything else. At the end of the meal we got a bill for our drinks and the mushrooms. By the way, the CM let us know up front that the mushrooms were not covered under the plan. I'm sure it's the same for spinach, etc.if your entree doesn't come with it, it's extra.
It's the same thing if you order mushy peas at Rose and Crown or a side of those mashed potatoes at Raglan Road.