Is it useful to have a 3 to 6 month supply of non-perishable food and potable water?

Maybe. If you can afford to do this for your family it is an ongoing sense of well being. So, even if there is a power outage and you are caught by snow or flood or wind or another emergency, your family has the non-perishable food and water to survive this calamity.

The things I have been writing this morning lead me to this conclusion. But, if you are already on the edge financially it might be counterproductive to do this. This is for people likely more that own their own homes and land who can afford to set aside non-perishable foods and potable water for themselves, their children and their grandchildren for emergencies. Also, be sure to keep looking at the end dates for foods too so you know when to either eat them or throw them away too. So, if you are going to do this remember it is quite a commitment to yourselves and your families ongoing. So, before you do this think about all the ramifications ongoing regarding all this.

I think the last time I personally prepared at this level was almost 20 years ago now during Y2K worry. We wound up eating most of it before it went bad then. But, it also discouraged me from doing this again because of all the work of getting it, storing it, using it, checking dates and using what we could of it.

So, I found this kind of difficult and not really useful then (except for less trips to the markets) while we used it up over time.