You can also save some large cans and spray paint them black. (Most of these had held kidney beans or spaghetti sauce.) Use black High Heat Grill paint, you can find it in the spray paint aisle of any hardware store. I just lay the cans and bottles on the grass and spray them. ( The grass gets mowed later and then the evidence is gone.)
You can use these instead of pots and pans inside your solar oven.