Perhaps the simplest upcycling material is the can, which, fortunately, comes in all sizes but is usually the same basic round shape. Cans have become so ingrained in our society that no one alive today can remember a time without them, and they hold everything from soup to soda pop, cooking grease to motor oil.
If Rome was built of marble, we could almost say that the Western world of today was built on the can. However, without industrial machines, cans are quite literally impossible to make. If the machines break down, along with society, the production of cans will cease.
Fortunately, there are millions upon millions of cans around already that could last for decades before rusting back into the earth. Cans made from aluminum can be crushed—but they could last long enough to see the rise of the next sentient species!
The point is that preppers should have a "can-do attitude" and know that a can shouldn't just be seen as an old container. Consider it, like its cousin the jar, a place to store items. Because cans don't break as easily as glass, cans can also be used as tools, and large coffee or paint cans can be used as shovels. In addition, teeth can be cut into a can to transform it into a large hole saw.
Many paint cans still have handles and, when cleaned out, these cans can be used as buckets. Old cans can be tied together with a string to create a primitive perimeter alarm system. This can even be enhanced by adding some small rocks to further create a rattling sound to warn you and/or scare off predators and intruders.