Handling packing material costs
At this point, packing materials cannot be associated directly with an order.
Packing materials for shipping are generally recommended to be tracked as an in-direct (supply), so they are not included in your COGS calculations. You can consider adding a purchase category to better group your packing expenses together for end-of-year reporting.
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.