One of the most useful substances one can use outdoors is Survival Cement.
This mixture of mud and grasses can be used for a multitude of projects, from construction of shelters, cooking structures, kilns and food caches, to wrapping food for clay baking (as seen in my articles on these subjects in Wilderness Way magazine ) and much more. Survival cement has been used throughout the eons of history in countless ways.
It is simple to make, the ingredients are easy to come by and it is one of the most durable resources available in a primitive situation. In fact, during a trip to Utah a couple of years ago we encountered some Anasazi ruins that were many hundreds, if not thousands of years old where the survival cement was still intact. (See photos below) How many modern buildings will be able to say that?!