Barcodes are a great way to speed up your order lookups and packing of products.
You can include barcodes in your templates by doing the following:
Login to Order Printer Templates (Shopify admin -> Apps)
Click the "Customize template" button on your design
In the editor, go into the "Options and formats" section
Scroll down to the "Barcodes" section, and enable the checkmark for order barcodes and/or product barcodes: