How to add weight to the total weight of the order witn Commerce Shipping with rules? I want to add a constant weight to the total weight of the orders in my shopping cart to account for packing materials in the weight calculation.

I'm also using Commerce Shipping Postal Code Code Weight. The Postal code weights work brilliantly.Shipping Postal Code Weights

What I want to do is add a 6oz to the total weight of my order.
You should implement this hook in a custom module:

/**
 * Allows modules to alter the weight that has been determined for an order.
 *
 * @param &amp;$weight
 *   The weight field value array representing the weight of the order or NULL
 *   if no weight has yet been determined.
 * @param $order
 *   The order object whose weight is being determined.
 * @param $unit
 *   The unit of measurement to use for the returned weight of the order.
 *
 * @see commerce_physical_order_weight()
 */
function hook_commerce_physical_order_weight_alter(&amp;$weight, $order, $unit) {
  // No example.
}