The main item for sale in sex shop is movies. Nowadays that’s usually dvds although you will see blurays and VHS videotapes for sale.
The second biggest item is what I guess you would call devices - the various things people use during sex like vibrators, dildos, lubes, role-playing equipment, costumes, etc.
Most stores also sell magazines. But magazine sales are declining in porn just as they are in the mainstream. Sex shops also, as I mentioned, often sell porn books.
Moving outside of sex products, a lot of sex shops also sell drug paraphernalia.
The closest thing I can think of is the adult section of the video rental store, which had a little curtain to keep the innocent passers-by from seeing in. It was not a very large section. Somewhere around age 19, I figured that since I was an adult, I ought to at least see what was there. I would never have actually rented one, though. (For one, I went into that store several time a week and was on a first-name basis with everyone there. For another thing, there was enough Internet even in those days.)
It has been a few years, maybe around 8 of them. It was to buy some toys with a person I was dating at the time.
For those of you who use the internet, don’t you get slammed with catalogs, etc.? I ordered from a company many, many years ago and it seemed every week there was some new not-very-discrete mailings from the company and others in my mail. Not cool! Haha