If you want few other items, just "add to them to your cart." (I know this works on a PC not sure if it works on the phone app. as I have had people complaining the could not find "Request Combined Postage"
"Then select View Cart" or "See in Cart" (Obviously don't pay yet) Then select "Request Combined Postage" I will then work out the cheapest and best rate for you, or you can email and request what service you like. If International, you may want a premium service within 10-14 days or by sea (Cheap) a couple of months!