Here's Finnish guide for this

It's not specifically for war, but for any disruption the society might have. We've had winter storms which cut power for few days, wildfires or floods can leave you stranded for a while, a lot of snow might cut roads and so on. Being generally prepared to be self-sufficient for few days just makes sense. On a bigger scale it also helps rescue workers if everyone isn't in immediate crisis after 24 hours without working infrastructure.