When I was in high school I worked as a picker-and-packer in the warehouse for a small online retailer. I would receive print-outs representing each of the orders that came in for that day; I would pick the items for each order from the warehouse; finally, I would pack the items and prepare the boxes for UPS pick-up. It wasn't a glamorous job, but it did help me pay for college.
During this job I was first introduced to the wonder that is the barcode - which is today celebrating 57 years since its original patent. The barcode allowed me to verify that I had correctly picked each order and ensured that nearly no box would be packed with the wrong items. The barcode enabled a teenage kid, like myself, to pack thousands of dollars worth of goods per day with nearly zero error.
The barcode is a silent innovation that has increased efficiency and decreased the number of overall mistakes made in not just shipping, but in many other industries. It is one of the unrecognized requirements for hugely successful ecommerce websites (such as Amazon.com). It is still extensively used but often forgotten - at least for one day, the barcode was finally appreciated.