I love the advice of DR--in an emergency/survival situation, NEVER throw anything away. I go camping with the Boy Scouts often, and it takes some doing to convince them of the wisdom of this.

Case in point--we had all gone camping and taken canned soup, stew, etc for dinner. After dinner, some had hot chocolate mix packets and wanted hot chocolate, but they hadn't brought a pot to heat water in. I showed them that the cans in the "trash" could easily be cleaned out and then set directly on the fire to heat water. They thought I was a genius for showing them how to do this; I worried about the fact that something so seemingly obvious wasn't--at least not to them.