Well, its hard to foresee how something like copper will be valued in a crisis time. If the value goes up so much that you get more than 50 cent for a copper penny, people will go and scavange all kinds of places for it. And it can be found in lots of places, because of its use as electric cables. There are people here who do this already now, although you only get 6 or 7 dollar for a kilo scrap Copper.
I think Silver is a better metal for bartering, and you can cut a 1oz coin in pieces for that if needed.