Ok, I'll try to explain what I want to do.

My shop sells scrapbooking paper 35 x 35 cms square
These papers fit nicely into a Pizza Box.
I can fit quite a few into a Pizza Box.

What I want do is add the Pizza Box to my shipping calculations (I use Auspost module so it is using WxLxH and Weight). I only want one box added no matter how many sheets of paper the person buys.

So basically if someone buys scrapbooking paper (1 or x amount), 1 Pizza Box gets added to the order as pakaging).

Hope that makes sense and also hope there is a way to do it.