Thanks for the mod writeup, a DEFINITE help.
The one change I made was to add a button to the main '/admin/orders.php?mode=search' page that says "Packing Lists for Selected" (right next to the "Labels for Selected" button) so you don't actually have to view an item to have the link to print the packing list. It involved a couple more lines of code and a little extra logic but I think my client will be pleased.
Cheers!