do some people seriously not have even a mere 72 hours of supplies? I can forget to leave the house for far longer than that.
More people have 72 hours of food, but perhaps not all the time. They might buy a week's worth on Monday, but by Saturday they won't have 72 hours left.
It's also not uncommon for European city-dwellers to buy food more frequently. They have less storage, and they can buy fresh food every day. The French are famous for buying bread every single day. (I once asked a French AirBnB host if she could leave two days worth of bread for me, since I had to be up super early on the second day, and she looked at me like I had two heads.) Others have practically no kitchen at all, and eat all of their meals out.
So for the humans, you don’t need any food, and for the pets, you probably have it anyways.
(And also, some pets are arguably low-priority in a real war situation. Cats and dogs maybe not, but stuff like guinea pigs might be.)
Because standard French bread doesn't keep, or at least does not taste as good, after half a day or so.
But the French will generally still have a few kilograms of pasta, rice, semolina and flour in their cupboards.
I have also never met anyone who ate most of the meals outside, except maybe a few particularly "social" students.
I literally have 72 hours of soda just sitting around. Hell, probably a few weeks of soda at least. There's also a bunch of pure water, too.
Also. You can go 72 hours without drinking any water at all... worst that'll happen is you'll get dehydrated, but dehydration isn't always immediately fatal. As long as you were drinking healthily before the 72 hours.