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.
Carry ice picks (more like ice awls) with you when you travel on ice. If you fall through ice turn back to the direction you came from and start breaking the ice with your elbows (no use trying to get up as long as the ice is so brittle you can easily break it), then drag yourself up and start rolling away from the hole and trace your steps back. Also, try to get rid of the wet clothes as soon as you can.