We buy most of our meat at Costco and are happy with the quality and the price. We use a lot of beef. We buy whole strip loins and cut them into steaks, whole beef tenderloins that we trim and cut into steaks. I can't remember what we last paid per pound/kilo for those, but I know it is considerably cheaper than the pre-cut, pre-packaged steaks at Costco. For example, the last whole sirloin tip, which we use to make our own ground beef cost $5.79 per kilo or $2.63 per pound. That's much less expensive than the extra lean ground at the supermarkets here, and it's of much better quality.
Mind you, we have two large freezers in the basement, so we're able to buy in larger quantities.
Produce, in general, I find prices are similar at the supermarket most of the time, and I'm not forced to purchase the same quantity. I don't always want to purchase eight apple pears, for example. Romaine lettuce and baby spinach are two exceptions. Much better prices and we use a lot of both, so the large packs are worth it.
All of the things you mentioned, Boomerang, definitely better prices at Costco.
I don't buy "fresh" fish there anymore. We've had problems with it being "off" a few times. No problems with the frozen fish, though. Lots of variety, too, on the shelves.
Books, hardcover and paperback, if you can find what you're looking for, are much cheaper than in the book stores.