I buy vinyl tablecloths when I see them on clearance. They are about the right size, and will last for years. Since they are a bit heavier, they don't blow about in the wind as badly as plastic.
I keep one in the back of my car for hauling plant purchases, or as a rain poncho or for picnics on the ground. The only problem with the tablecloths is that weed seeds and prickly leaves can sometimes stick to the cottony side.