I shop at Costco and use the stuff up pretty quick - except for, like you said, cans of tuna that sit in wait for their moment to shine rescuing me when the fridge is empty. ; )
But it can be 'consumerist'. Studies show that the more that is available for people to buy, and eat, they more they will buy and eat. I may not be saying it well - but in other words, one thing that Costco does is inflame appetites because people see "OOOOOHHH!!!! Look at all that I can buy" which is, in part, why they are successful. Of course, all stores do that, Costco at a higher level.
But their prices are great, and if the price isn't better, the quality is. And because they treat their employees well, they are usually happy and quite efficient at their job. AND you can buy a huge 'everything' pizza for $10. YES!