The first truly portable devices were tape based although quite a number of smaller radios did have earphone sockets as the one I had during high school did which I used a lot and I can recall my second best friend at high school getting her tape device, it was a Sony Walkman quite well with a mains unit which in some ways restricted the idea of being just anywhere but in the days before rechargeable batteries were common, I could see the savings over changing the batteries every ten or more hours.
The first one I got was around 1985 having gotten that other entertainment essential of that era , the large stereo radio-cassette recorder to listen to the radio on and play your tapes on and mine was an Aiwa.
It was this, an Aiwa HG-G35 which automatically changed tape sides when you came to the end of one and resumed playing the other which was a great boon not least when you were walking around although I always had to have a grown up with me anywhere near roads cos apart from the risks of not hearing traffic, my road sense is poor anyway.
It had a tape selector in case had tapes made on anything other than regular type I tapes and a three band equalizer to alter the tone with if you needed to and on the tapes I made you didn't.
The mechanism unlike later models was nearly all metal.
It actually sounded really quite good on a pair of good quality headphones, much better than a later Sony one I had did.
I had rather a lot of cute paper based self adhesive animal stickers on the front of mine that phazed some folks when I worked and a good indicator of how even in public my Middle with a little side was coming out even then but I wasn't bothered listening to Rush,Duran Duran and Five Star albums on Maxell type II tapes during breaks.
These days I have my Fiio player that plays digital files on Micro SD cards which technically is better but I loved the simplicity of that player.