The reason why craigslist is so successful is because people can buy anything depending on the need. So I am not sure if there is a way to quantify what people are buying "most". I would say "everything". Look at any "for sale" section. There are lot of ads on a daily basis. For example, I have bought furniture, laptops, cell phones, cars on craigslist but if I needed anything else, I would not hesitate. The only reason I don't buy on craigslist is if I need something new OR it is for my kids which I don't want used.