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.
I just carry a half gallon thermal jug with me all the time. Hiking or not. If my mouth feels the slightest bit dry, I need to drink more water. I tend to piss clear, or very pale yellow cause of this, but the upshot is that I was fine wandering around Anzo Borrego national park, and two of my friends (who thought that my idea of covering myself head to toe in jeans, a trench coat, and a trilby was a bad idea,) damn near got heatstroke. I basically threw my water at them when I noticed they weren’t sweating anymore.