There are definitely some items I don't buy at costco simply because I don't need that volume of food.
I have ten pounds of butter, none of it Costco (the local gas station sometimes goes nuts on sale). Reminds me of:
> The Costcos don’t want you to know this but the butters at the gas station are cheaper you can take them home I have 458 pounds of butter.
I used very little butter living alone and not cooking more than an average American, if not substantially less. I then got married and now have a family where we are cooking at minimum one meal per night, including some baking.
I'd be surprised if we didn't go through 4lbs of butter per week on average at this point. We typically sub butter in for most oils, as those oils were subbed into recipes during the anti-fat crusades a few decades ago. When you do this your consumption increases even further.
If you tend to not cook yourself or avoid animal fats like the majority of people I could see butter usage not being that high.
Butter also freezes indefinitely, so having less than 90 day supply on hand (12lbs or so) just seems irresponsible to both my family and society as a whole. Keeping even just 30 day stores of staple products seems to be a thing of the past in the US, but I feel it's setting us up for tears.
Edit: Others have already said it, but Costco is actually fairly bad in general for commodity items like butter or rice where you don't care about brand. You will likely find far better deals on "generic butter" at your local restaurant supply store, or even just regular sales at your local supermarket. Ethnic stores for things like bulk rice will almost always be substantially cheaper as well. Costco is rarely the cheapest unit cost, but it wins on convenience.
Where Costco shines are the few specialty items they run through way more volume than most such as imported Kerrygold butter and that sort of "upscale" branded items. Their white label booze is also substantially cheaper for better than average quality as well.
Yeah, I guess that's the rub for me. I will generally use olive/vegetable oil whenever possible and I don't cook to the extent where I have a bunch of unavoidable butter recipe's to begin with. I keep a small bin as a general "just in case" measure but I sometimes don't even go through that.
Also only have a small freezer, so the thought of freezing butter simply never occured to me.
"raises hand"
Good quality butter at a cheaper price. We freeze it and it lasts a long time.
I don't go to Costco "first" in most cases because trips there are far less frequent than regular grocery-store trips. I keep a separate shopping list for Costco, which includes the core items I've been buying there for years. When the list gets long enough, I make a special trip to Costco to restock. That's why it's infuriating to find that a bunch of the items have suddenly disappeared.
I will say that what remains on my list has been pretty steadily available for some time now, with occasional outages. There are quite a few Kirkland products on there. Their peanuts (in the white-labeled metal cylinder) are outstanding, for example.
But other things that look like stapes can come and go, some seasonally, some after a few years.
Costco is a very "go first" store - you go there, get what you can, and then flesh everything else out at some other store that will keep things in stock even when they get pricey.
Costco is also not the cheapest, not by far, but they are the most consistent.
Butter and soda are two of the most noticeable for me, you can easily beat Costco on both, butter because local producers often supply local stores cheaper, and soda because it's a loss-leader in many places. There are others, find them!