Remember the 128 pounds of pasta I purchased for my food storage last weekend? I purchased 170 packages of the pasta in 12 oz packs for 38 cents each. That cost me $64.60 for the lot. I was at the store today and noticed they were still "on sale" for $1.00 a pack (I think the regular price is about $1.30). If I purchased the same amount today, it would cost me $170. That is a savings of $105.40 off of today's "sale" price!
Goes to show, just because something is on sale does not make it the best deal. One needs to know the price of the items you use on a regular basis to know if the "sale" is really a good deal! Generally, grocery stores will have "loss leaders" most weeks to entice shoppers to come in and hopefully purchase other items at the regular price (in case you don't know, a loss leader is an item the store will have on sale at cost or at a price lower than what it costs them to purchase it from the distributor).
If you do your homework, you will realize savings over time as you build up a stockpile of staples you purchased at rock bottom prices! The object is to buy enough so you don't have to purchase that item again until it goes on sale the next time. I'm still learning, but it is fun to notice the inflated prices of items already in my pantry I purchased at prices much lower than what they are sold for today!