One of the most important items for any emergency kit is a good emergency blanket. By their design, emergency blankets are designed to help preserve body heat in situations where external heat is not available and weather conditions are cold. By retaining and circulating your body heat, the emergency blanket will help keep your core body temperature up until the emergency situation passes.
This product is like a parachute, if you need it but don't have it, it's too late. I'm a frequent winter hiker, and this affordable item is certainly a savior. Lightweight, effective, under $3, and can potentially save your life; you can't possibly go wrong.
I got two to carry around in each of my vehicles this winter. Cheap insurance in case I'm stranded. It's a plastic sheet so at least they could be used to keep things covered and dry.