Macworld Savvy shoppers spend their dollars at Costco, a members-only warehouse with bulk grocery and household finds. If you want to experience greater savings and convenience, you can sign up for a Gold Star Membership here ($60 per year) and get a $20 Digital Costco Shop Card* to spend. Costco has more than 500 warehouse locations across the U.S., but you can also explore their online selection at Costco.com. You might find groceries, electronics, baked goods, clothing items, and pantry staples with both brand-name labels and Costco’s brand, Kirkland Signature™. Costco backs just about ever…