I was thinking about that when I was dropping my 6 year old off at some hobbies earlier - it’s pretty much expected to have learned how to ride a bicycle before starting school, and it massively expands the area you can go to by yourself. When she went to school by bicycle she can easily make a detour via a shop to spend some pocket money before coming home, while by foot that’d be rather time consuming.
Quite a lot of friends from outside of Europe either can’t ride a bicycle, or were learning it as adult after moving here, though.
edit: the high number of replies mentioning “swimming” made me realize that I had that filed as a basic skill pretty much everybody has - probably due to swimming lessons being a mandatory part of school education here.
In the dry SW US the answer is drink water when it’s 100F or worse 115F+. Having a half liter of water from the hotel for the half day mountain hike, or pounding a half gallon of ice water and throwing up five minutes later. Your body doesn’t tell you when you should drink, it tells you when you are already behind on drinking.
This is no joke. Even experienced hikers won’t bring enough water for their trek and will end up either being emergency heli-evac’d out or just plain die.