Baluard bakery is situated on the street of the same name in the heart of Barceloneta, near the market. The line sometime stretches out of the door as locals know that the bread is worth the wait. Try the baguette made with olives. They have some great ready made sandwitches too if you need lunch in a snap.
You'll get a taste of local life and some of the best bread in Barcelona at Baluard. Bread is made on site and you can see the ovens in the back. Set in the heart of Barceloneta you can make a pit stop here on the way to the beach and avoid the tourist traps.
Try the almond croissant if you have a sweet tooth.