In case you are placing a larger order (with more than five items), the cart is behaving very badly and may even time out, deleting all the items in the cart. Smaller orders seem to be coming through fine in my tests. It is the number, not size, of items that seems to cause the glitch. The cart developers are aware of the problem and working on it.
One possible work-around would be to place two smaller orders, one with the shipping option you prefer selected and the other as if it was a "customer pick-up" order. Then send us a note to combine the orders. If you have any trouble , just email us at email@example.com and we will get back to you as soon as possible.
Thank you - Maria