Yeppers, what they said!
I'd say that the first thing would be to identify WHY you want a stockpile, and what kind you want. For me, my "stockpile" is just a really a pantry on steroids. I buy what's on sale in enough quantities to last me "a while" while not taking up too much room. And then there are the people you've seen on extreme couponing where they have 188 rolls of paper towels... And there's everything in-between.
So do you want to stockpile to save money? Then buy extra of things whenever the prices are lowest. Example, I combined a sale and a coupon a few weeks back that brought the cost of manwich down to about $.33 a can, so since the use-by date was 18 month away, I bought 18 cans, since we're unlikely to eat manwich more than once per month. But that's why you'll hear people talking about "price books." People track local prices to know WHEN to buy 18 cans of something...because just because the store says "SALE!!!" doesn't mean it's a good price.
On the other hand, if you want a stockpile because you live far outside of town, then you're more interested in a large quantity than in every single item being on sale-- the point is to save gas and not run out.
If you're worried about the apocalypse, you'll be more interested in very-long-term storable stuff, which is an entirely different deal.
I'd say a good place to start is figuring out what the sales cycles are for your area. Around here Safeway and Aldi change on Wednesday, Giant changes on Friday but releases their new ad on Thursday, and CVS changes on Sundays, releasing their ad on Friday or so... Knowing before the current sale ends what the next sale will be helps you decide whether to buy now or to wait. And getting the "weekend edition" paper on Saturday should get you the coupons that most people won't get until Sunday morning, which can help you figure out if there's something worth going at-opening-time.
Some people (who are WAY more dedicated than I am) have figured out that toilet paper goes on sale every X number of weeks and they buy enough to last to the next "big cycle." I don't do that... BUT when you get a coupon circular, don't throw it away until EVERYTHING is expired, even stuff you think you'll never buy... SOMETIMES (rarely) things that aren't a great deal usually will go on sale weeks later, and when you buy X amount, you get Y back... CVS does this a lot with P&G items...
And, first and foremost, promise yourself you won't overbuy a bunch of junk you'll never really use. Even if you're lying, promise yourself.
It's not a good deal if you'll never use it.