The wife and I tried to do it at the regular grocery store (with incorporating coupons), but it was an uphill battle and expensive.
A word of advice is to familiarize yourself with price per unit. Sometimes a "deal" at COSTCO or Sams isn't. I had a hard time getting over the $50 membership fee to shop at COSTCO, but after 4 trips I easily saved twice that (we did A LOT of stocking).
Also, once you have a good litte supply going it is easier to add to. Just remember FIRST IN FIRST OUT. They have FIFO things (like the soup can displays at the grocery tore only smaller) at COSTCO for about $20 to make it easier and save on cabinet space. We bought one each trip to lessen the impact of dropping $20 a pop.... we thought in turms of this is 5giat jars of p. butter, o 4 sheets of canned corn etc.
You can also order Mylar bags and food buckets for flour/sugar that will help keep these items for 10 yrs or more..... and it doesn't hurt that COSTCO sells flour and sugar i 25 and 50lb sacks.
Key words of advice..... don't go broke doing it and try to avoid running up the credit card unless you think the credit agencies will all go broke/busted in next week and the power will go out and all of your bills erased.
That said YOU CAN find good deals at the grocery store and coupons (especially stores that double/tripple) can help with costs. Also, some places like Walgreens have reward points that you can use to purchase items (free or super discounted prices). Their are other blogs out there that explain how to do this (moneysavingmom?). No, you don't need 12 bottles of shampoo (while you rack up rewards points) but you may end up uing them later and at $0.25 is it all that bad?
Also, you mentioned a lot of other people in your post. Get it into their mind now they need to stock up. Tell as FEW people as possible that you are stocking up (word travels fast that you have planned). If you are intending on supporting others... make a short list and stick to it. The last thing you want is the SHTF and 30 people show up at your door. Then you try to support everyone and 2 weeks later YOUR family is starving.
Also, things like tobacco, alcohol, candy, shaving razors, and other convience/comfort items can be used to barter and trade with.... so it might be wise to grab extra of those.
Try getting the book "How to Survive the End of the World As We Know It." It is a good book for the BASICS (though some of the things he mentions aren't feasible for everyone and I don't 100% agree with). It will help you think ofthings you may need in a SHTF scenario (med supplies, hand tools etc). Once you have a basis...... make a list and prioritze. And then re-stock, replenish, add on.
Also, you may do well to find others that are like minded (CLOSE friends/family that may help split costs of big ticket items, but you are ultimately responsible for your family).
Hope this helps.... I'm sure others here have opinions too.
Most planning can be done by shopping locally. Depending on your income and storage space, you might only be able to stock up a few extra canned goods each time you go to the grocery store. Same goes for the medicine cabinet, hygiene and cleaning products, and don’t forget the pets. A little here and a little there will eventually set you in good stead. Be creative in finding storage. It’s amazing how much room can be found under and behind furniture. Plastic milk crates hold more cans than you’d think, then turn them upside down and cover them for extra seating in the kids’ room and no one’s the wiser. Don’t store foodstuff in the attic because of the temperature changes.
Now might be a good time for a spring cleaning and get rid of excess clutter (just tell the family they need to help spring clean and don’t mention your prepping). That will open more storage space. Have a garage sale and use the profits for your prep so the family won’t complain about excess spending.
While cleaning out, don’t forget to organize. I know, it’s not fun but necessary and you’ll likely find you have more prep supplies than what you might have thought. Make a list of what you need to resupply and what areas you need to begin gathering information on.