You can find almost anything you might possibly want or need in Guatemala City [1]. In addition to many modern shopping malls stocked with the latest fashions and electronics, there are a number of department stores for household appliances and cosmetics.
For grocery shopping, the local giant is Paiz, which was recently taken over by Wal-Mart. You can shop in bulk and enjoy greater discounts at its Hiper Paiz mega-centers.
U.S.-style warehouse shopping is available at PriceSmart or at a number of local chains. Guatemalans love U.S.-made goods, which is easy to see given their wide availability.
Links:
[1] http://www.moon.com/destinations/guatemala/guatemala-city