I've already placed an order, but would like to add some additional items to it.

Please place a separate new order for the additional items. The reason we request this is that we select items for shipping to customers in the order that they originally placed their orders with us. Much of the merchandise we sell is only available in limited quantities, or may take weeks or months before additional quantities are available. In those cases, people have to wait. If we add an item to an order you have placed previously, you are in effect "taking cuts" into the line of people waiting for that item.

On the bright side, when shipping anything to a customer with more than one order with us, we check all their orders for available items and ship them together to keep shipping costs as low as possible. In addition, we only bring new orders into our accounting systems once a day, so orders processed in the same daily batch will be combined into one order anyway. At any rate, when you place an order with us, try to add everything you can think of before you press that "submit" button!