Using OpenCart for in-person sales

The website I manage uses OpenCart, and everything is working great. However, once a year, they have a reunion, and sell a lot of merchandise in person as well. What is an easy way to still keep the stock and everything correct in OC, while making it fast and easy for someone to put the sale in? Right now it's the same process a user would go through: find the products, add them to the cart, go to checkout, put in all of the information. I'm looking for an easy way for someone to add what they are buying quickly, and quickly be able to checkout without having to give full billing information. Any ideas?

Someone recently released a POS system for opencart. Do a search for it.

Yes, and I saw that, but I did not see how it would make it easier and faster to get the products chosen and the checkout done without needing full billing information (I would just like to be running the cards)

try the latest standard version. An order can be created by one click without entering full billing information