At Barcelona's iconic Corte Inglés in Plaça Catalunya, shop for high-end clothes, shoes, housewares and accessories. They have a fairly reasonably priced souvenir section, and their gourmet grocery area has amazing eats from all over Catalonia, Spain and Europe. Looking for something from home or products for people with dietary restrictions of some sort? Chances are you'll find it here (but it'll cost you).
After you've all but melted your plastic money, settle in for a drink or something to eat in the store's top level bar for sweeping views of Barcelona.