The correct answer is "pneumatic tubes."
What was not a feature of the post-Civil War department store was "pneumatic tubes."
After the Civil War ended, there did not exist the technology to develop this device. All the ticketing, management paperwork, and accounting were delivered by hand.
After the American Civil War, department stores started to be more than a place to purchase things. People, especially women, made this place a center to "talk a walk," distract themselves and even socialize.
Let's have in mind that when the war ended, President Lincoln ordered a quick Reconstruction process that was followed by President Jackson after President Lincoln's assassination.
President Lincoln supported the Ten Percent Plan to readmit former Confederate states to the Union because he wanted to heal the wounds of the Civil War as quickly as possible.