Probably the most important skill people are skipping is etiquette. Which I think says a lot about HN. Communication (texting, listening, etc), maintaining and creating relationships, avoiding injury, relaxation, exercise, cooking, healthy eating, self defense, first aid, swimming, types of reading (fun, searching, learning), searching, separating truth from fiction, knowing when to seek help, a hobby, cleaning, main…
For instance, saying “excuse me” before you barge in front of someone to get something off the shelf at a shop. I’m American, so that is obvious. I live in Estonia, and here you either 1) stand awkwardly and wait for them to move because you don’t want to interact with them or 2) just shove in front of them and grab what you want and leave.
The first time I took my then girlfriend to the UK she did that and the woman she dove in front of looked at me like “WTF?”. I apologized and then had to explain to my girlfriend that that isn’t acceptable in English-based countries. She was genuinely confused and asked how she should do it instead. Even though she speaks English fluently, there is only so much you learn from Cartoon Network (I kid you not, many have learned English that way) and YouTube. She wasn’t trying to be rude, she just genuinely had no idea it was coming off that way.
The same also applies to standing in lines, getting on and off public transit, and many other things.
Edit: oh, and table manners. My $diety, the table manners... I don’t expect you to be able to set a formal place setting (though I can), but we aren’t animals, you should know how to use a napkin, not to double dip your chips, etc.