I have a tendency to buy household items in large quantities. Part of it is the idea of taking advantage of a good deal, part of it is having the space to store the haul, and part of it is a dislike of running out of things that we use every day or regularly.
Costco and the other warehouse clubs encourage this approach with the way their items are packaged. You want this cleaning product? Well, you'll have to purchase it in this bulk-pack. At the moment I have an eight-month supply of laundry detergent that I purchased at Costco a couple of weeks ago. It's their store brand, Kirkland, and it comes in an enormous squared jug that sits on its side with a spout on the bottom.
But I do this when shopping for other household stuff. I almost always buy two tubes of toothpaste at a time, or two sticks of anti-perspirant, when I go to Target. I'm already there, it's a good price, and I know I won't have to go back so soon for more. Target has the best everyday deal on tissues that I have found: four boxes of store-brand, 200 per box, for $5. Tissues are one of those items that are almost universally overpriced, so this helps avoid that pitfall.
A few weeks ago the Mrs. returned from a trip to CVS with 52 rolls of toilet paper (two 20-packs and a 12-pack). Normally we buy it by the 12-pack, but CVS was offering a $10 gas card to those who spent a certain dollar amount on certain products. (I am curious to see how long the 20-pack lasts in a household with only two adults.)
However, this purchasing behavior does not always extend to food. We try, but we have to be selective about the purchases. We can't always justify bulk food purchases because we often won't be able to use whatever it is before it spoils, which ends up wasting money, which is the opposite of what we're trying to do.