1 cup sourdough starter
Whole wheat flour — bring a lot
Knead enough flour into the starter to produce soft dough. Sprinkle the dough using more flour. Bring the dough in a plastic bag bearing a cup of dry flour. Keep the bag tightly shut. Sourdough starter should be mixed with flour because it could only be stored in liquid form in glass or ceramic containers, which are so heavy and inconvenient for camping. The starter would keep a week or more. Maintain the starter fresh by feeding and using it once a week or more.
To use this starter: put the soft dough starter in a bowl. Add 2 to 4 cups of warm water and 2 to 4 cups of flour. Put the bowl in a warm place 3 to 4 hours or overnight (close to a warm fire in the winter). Now the starter is ready to use with whatever sourdough recipe.