A haybox or straw box is a primitive cooker that utilizes the heat of the food being cooked to complete the cooking process. Food items to be cooked are first heated to the boiling point, and then the stove / oven / fire or other heating method is turned off. The food is then transferred to a highly insulated environment inside the haybox. Over a period of time, the food items cook by the heat that is trapped in the insulated container. Generally, it takes three times the normal cooking time to cook food in a haybox.
Hayboxes are extremely efficient ways to cook certain food items, particularly if you have the time. They help conserve energy by allowing you to turn off your stove or other cooking source and just let the heat you've already generated do the rest of the cooking for you. For example, items that take a long time to cook like rice or beans make a perfect haybox meal.
Most slow cooker or crock pot recipes can be adapted easily to use in a haybox cooker. A good source of recipes for all retained heat cookers can be found on this weblog: http://thermalcooker.wordpress.com/category/recipes-all/