Commonly polypropylene, polyethelyne, polyvynil chloride, polyolefin.

As the plastics industry loves to remind us (using very expensive TV ads), plastics are important. They keep food fresh, and they're essential in medicine.

Of course, a lot of plastic is used for things that have nothing to do with either one of those things. Many of which are, in fact, incredibly stupid and irresponsible, since making plastic requires lots of non-renewable resources (i.e. oil), produces lots of toxic byproducts which are rarely, if ever, disposed of properly, and, best of all, plastic is never going away. It is not biodegradable. Or, in simpler terms, we're going to be clogging up landfills with it for millenia to come.

Few things, however, are as awful as shrink wrap. Shrink wrap, unlike some other plastics, is almost never recycled. Virtually nothing shrink wrap does for non-perishable products cannot be done, for roughly the same money, with an alternate material... for instance paper, or my personal favorite, nothing at all.

Also beware shrink-wrap's demon spawn, the shrink-wrap license.