For a quick and dirty portable whiteboard, wrap a book in aluminum foil

CaptionThen scrunch it around the sides to fix it in place. Dry erase markers will wipe off just like a normal whiteboard.If you get any creases, you can flatten them down with your fingernail. It's not perfect, but for a few pennies worth of foil and ten seconds of work, it's not half bad.As an added bonus, if you want to hold onto your current work instead of erasing it, you can just swap out the foil.