Handling packing material costs
At this point in time, packing materials cannot be associated directly with an order.
Packing materials for shipping are generally recommended to be tracked as an in-direct (supply) expense, so that they are not included in your COGS calculations. You can consider adding an expense category to better group your packing expenses together for end-of-year reporting if need be.
If the materials are part of the presentation of your product (i.e. a presentation box, sleeve or bag which are packaging materials), then this could be considered part of your COGS and could be included as part of your recipe and manufacture process.