I think you can do that with custom labels? But that's at the "Silver" level.
So, just to help us better understand, would this idea work best for you if it automatically printed whenever an order came in? So, say, an order comes in on Sunday at 4:00 a.m., it should print then. Or would it be better if whenever you log in to ShipStation and have it active that you would prefer to have the packing slips printed out then?
I spent an hour on the "automation" screen trying to figure out how to do exactly this. Whether it's on a schedule or not, I don't care.
I'm using Shopify and selling a single SKU, but when I print my Packing List or Order Summary, I'd like to be able to see a full list of each of the parts that need to ship as part of that product. It's very important that I can include the list of parts on the printed reports.