One of our favorite Brazilian luxuries is the abundance and diversity of fruit available for consumption. It really is not a luxury, because the fruit is insanely cheap to buy (i.e. we bought 10 guavas for $2 on a street corner), but you do have to travel outside of the U.S. to indulge in this nutritional goodness.
My second favorite luxury is the plethora of walk up juice bars on every corner of the Copacabana, Ipanema, and Leblon neighborhoods. You just walk up, order from the never ending list of juices, drink your juice, chat with the other juice patrons, and get your 5 servings of fruit in one sitting.
El Camino recommends the juices of Bibi Sucos in Copacabana (though there are locations throughout the city) and specifically the "Suco Verde."