We have Costco and Sam's memberships and I go almost WEEKLY! It is a huge help with teen boys. I prefer Costco...over Sam's. We got a Sam's membership for $5 through Tmobile.
I use it to buy almost ALL of my groceries...fruit is a big one, cheese, sodas, chips for lunches, uncrustables, bacon, paper products, eggs, water, trash bags, meat, spices, rice, baking supplies...really almost everything.
The only thing I get at a regular grocery store is bread (we don't eat a lot of it), certain cereals, milk (don't drink a lot of it) and ice cream