When I travel abroad one of the things I miss is Polish bread :). We have a really great tradition of baked goods. Galeria Wypieków Lubaszka reminds me of the times when I was a child — my parents always bought pastries there. Now it’s quite a big chain of bakeries in Warsaw.
At Lubaszka there is a real wide variety of breads, buns and cakes. From the breads, I recommend e.g.: chleb włoski (Italian bread, also with olives), staropolski (traditional Polish bread) or urodzinowy (‘birthday’ bread). You can try there typical drożdżówki – sweet yeast bun, usually with some filling like poppy seed, blueberry, pudding or curd cheese. They also have good cakes and tarts for reasonable prices, e.g. sweet loafs, fruit cupcakes or meringue tart (my mum sometimes buys one just for herself and eats it instead of dinner ;)).
In some of the shops, like at the one on Krakowskie Przedmiescie, you can also have fresh carrot juice. I also recommend the sandwiches with egg or a slice of pizza (often straight from the oven).