Medicine (350 generic zyrtec for $15), meat (ground turkey, amazing lamb chops, organic chicken breasts), fruits and veggies (double or triple amount for the price in grocery store), Kirkland eco-friendly detergents/cleaning supplies, almost any Kirkland product (EVOO, organic maple syrup, spices, olives, artichokes, lunch meat, etc), cheeses, golf balls, sunglasses (polarized Ray bans, etc), eyeglasses/contacts.
My wife is the shopper and she says the advantages over Sam's are more healthy and organic options, better quality, and not everything is sold in massive bulk.