It’s also reasonable to look at it as a “the populace goes nuts every time there’s some minor shock to the logistics chain, so might as well prepare for that reaction”
Yeah, there doesn't need to be a shortage of toilet paper to cause problems, just the fear that panic buying might start so you better stock up before they hit. It's basically a prisoner's dilemma, you know you shouldn't panic buy, but if you don't and other people do it's rational to do it.
What would be a signal that you should panic buy to beat the rush? A drone shot down over Poland? Article 4 being invoked? What if a falling drone causes a casualty?
Simply having deeper stocks will let them avoid the empty shelf photos that can tip the balance into panic buying.
In the USA I try to have what we need for one week with food and without power or potable tap water. This just seems like common sense. After the SF earthquake in 89 you weren't supposed to drink the tap water for a couple days. Lots of things have taken out power and COVID made shopping difficult. Resilience is good.
3 days is a pretty long time unless the damage is catastrophic and very broad based. Extended preparations come with an overhead cost that must be offset by the benefit.
Denmark specifically is not a populous country. You could probably keep the entire country fed with just the capacity of e.g. the US military airlift capability, which has been used in these situations. The emergency reserves mostly only need to exist until supply chains are established. It is a balancing act.
Given people are already advised to stockpile for at least a week if not two, it's both deepening the resiliency capacity for all, and providing capacity for those too poor (either cashflow-poor or housing-poor) to stockpile.
