Hardtack is a dense bread that has minimal water and can last months without modern refrigeration. It is true to its name and has a reputation for being hard as brick. Historically, it has helped armies and sailors make long trips by packing wooden casks with this hard bread.
Making it is simple and it requires only whole wheat flour, salt and water.
Next, measure 2 cups of water and dissolve 4 teaspoons of salt into it.