I was just doing my online shop last night. So many items like bottled water and long life milk were out of stock.
Quite clearly many people are taking the advice seriously. But to be honest, three days’ worth of food is really very little - most people would have that at home, even if it may not be their preferred food. So I think people are responding to this by buying supplies for a lot more than three days.
Full disclosure - I have done this myself. Not buying silly amounts but just a few more cans than usual. I don’t even know why!