Before the 1950s, companies didn't target "teenagers" with consumer products as much. Many non upper class folk had to grow up fast from being a child to being a worker. After the post-Second World War commercial boom, there was a new demographic of "teenagers" that went to high school, earned an allowance or worked a job, and had free time and money to spend.

2000 years ago, there were not factories to mass produce the exact same product for many people. Its possible that there were some "must have" or "fad" items at different times and locations, but it would not have been as widespread.

perhaps fashionable young person might be a more useful term then "teenager"?

What would be a must have item for a fashionable young person of some means 2000 years ago. What about a great deal of means.