I want to cry.   Sales Receipt is not a solution for creating Packing Slips because you cannot create one from an invoice for the transaction you want to ship against!  Sales receipts are just another way to book revenue from a customer (immediately), therefore using them will double count the transaction.   :-( 

So the only solution for users who want real packing slips is:
Intuit to get off your arse and implement customizable form for packing slips!   If you are unsure what features to provide, ask me your other B2B business users!