For Kirkland brands, TP, PT, Laundry pods, coffee k-cups n seaweed snacks are always on my list. Extra virgin olive oil, grape seed oil, balsamic vinegar too but don’t expect top quality/flavour. Still good for day to day cooking for most.
Non-Kirkland musts are Steinfeld pickles (the best out there IMO), tonkatsu ramen bowls, bread, huge wedges of Parmesan cheese, 4 packs of bacon, born 3 eggs, avocados, cucumbers, asparagus and soy sauce. Other necessities such as mouthwash, toothpaste, Q-tips, contact solution etc. are good buys there.
Buy meat in bulk and portion it at home. That said, pound for pound, better deals can be found elsewhere depending on what you’re looking for when it’s on sale but Costco is usually a reasonably safe bet for stuff like ground beef, wings, chicken breast/thighs etc.
Welcome to the club. I don’t wanna brag or nothing, but I am an Executive Member