I am assuming what you are having trouble with is getting the same tracking number on both orders to prove shipping.?
Bring up the first item. Enter the combined weight and size for whatever package you are using (you put both items in the same box). Print your shipping label.
Then bring that same page up again and in the upper right corner more or less you will see a tracking number with a link next to it "edit". Click EDIT (not the tracking number). That will open a page with the tracking number. Copy it to your clipboard.
Then go back to your list of sold items and find the second item. On the left it will say "print shipping label;" DO NOT click that. Notice there is a small down arrow. Click the arrow and a drop down menu will appear. On that menu it will say "add tracking number". Click that then paste the previously copied number and "save".
That takes care of it.
"Laissez-faire capitalism (AKA The Great Material Continuum) is the only social system based on the recognition of individual rights and, therefore, the only system that bans force from social relationships." ~ Ayn Rand