Two from Australia, one boring and one genuinely alarming.
The boring one is bin colours. There are three bins, each with its own coloured lid and its own collection day, and I put the recycling in the general waste for a month before a neighbour left a very polite note in our letterbox, with a small diagram. My wife framed it. It's on the fridge.
The alarming one is magpie season. In spring, certain birds swoop at people walking or cycling near their nests, sometimes quite hard. Nobody told us, because for Australians it's so normal it isn't worth mentioning. My eight-year-old was swooped on the way to school and came home convinced we had moved to a country where birds attack people, which, to be fair, he wasn't entirely wrong about. The school sent a note home the same week with tips, as if it were weather.
We now walk a different route in September, and he wears his bike helmet with cable ties sticking out of it, which is apparently the local solution. He is very proud of it.