That's my thoughts too. Even before Covid, we've always had plenty of "supplies" in the house, not just food and drink, but also for other contingencies, too, such as a box of candles (plain white ones, not fancy decorative ones!), a battery radio, a pulse tone telephone, torches, a full range of batteries and light bulbs, multipacks of loo rolls and spares of toiletries and even a gas camp stove! Our kitchen cupboards have more than one of everything, we have a second "overflow" freezer in our utility room, always some frozen bread and milk in the freezer. It's just "normal" to us to replace what we use and buy in bulk when things are on offer in the supermarkets. We have a shopping list in the kitchen that we write on when we open the last of something or notice there's only 1 or 2 left of something we use a lot like a tin of a favourite soup or packets of biscuits, or canned drinks, etc. Same with our cars, we never let either car get less than half full of petrol.
I'd be pretty confident we could easily last 72 hours without really noticing, and probably up to week still eating/drinking our normal daily patterns. After a week, it would probably start getting a bit boring and difficult as we'd be having to eat/drink what was left rather than what we actually fancied. I don't think we'd start struggling until probably two weeks, but even then, there'd still be things we could cobble together.
I think, in my case, it's because I was brought up in the 70s with the power cuts, going to bed with a candle, not being able to have a cooked meal if you got the timing wrong, etc.
It served us well when our entire city's power went down in Storm Desmond a few years ago. Four days without electricity, and then another 4/5 days with power provided by road side diesel generators which kept running out of fuel or breaking down. So disrupted power for over a week. We were listening to the local radio on our battery powered radio, phoning family on our pulse phone, cooking on the gas camping stove, walking around the house with candles in jam jars. Lots of people really struggled, especially as it was weekend when it happened and the local authority didn't get their arse in gear with things like organising hot food catering vans on random street corners and distributing bottled water until the Tuesday! Shops were closed, petrol stations were closed, no public transport etc - it's frightening just how quickly "normal" life can be taken away from you and how slow it is for the authorities to swing (sloth) into action as there's really no urgency.
Obviously, also worked wonders at the start of Covid, as we already had our "stock pile" and didn't need to join in the madness of everyone emptying the shelves. We just sat out that mad week as we didn't need to go shopping, and waited until the stocks were replenished in the shops before we stocked up again a couple of weeks later.