Plastic may not be as indestructible as titanium, but it can provide basic protection from the elements in certain situations. For example, don't let a surprise rainstorm ruin your new shoes or soak your clothes. A plastic garbage or large shopping bag with a few strategic holes cut in it can double as a poncho. Grocery bags are particularly handy as makeshift galoshes. Simply step into the bag and tie the handles around your ankles.
If you're a gardener, you can also wrap plastic bags around your knees to cushion them and keep them clean and dry while you kneel over a flowerbed. Plastic bags can even thwart the efforts of an unexpected frost if placed over delicate plants the night before.
Plastic bags can also be used as a cheap and easy alternative to other household items designed to protect surfaces and valuables. Use bags as a litter box liner, mattress cover, drop cloth and dustcover for items in storage.