We've added a new setting to packslip configuration to show the sales order line item number. If you turn this setting on, instead of numbering the lines in the shipment by 1, 2, 3, etc, we will show the line item number from the sales order so that your customers can easily match up what's in the box to what they ordered. This can be turned on in System Data > PDFs & Email > Packing Slips.