Sunday Market at Gare du Midi is a must. It is a nice stroll through the different neighborhoods when coming out of the city centre.
I enjoyed seeing locals pulling their market carts behind them, the concentration of market carts grew when I was 0.5 miles away. Along the way I passed by many bakeries. It was hard not to step into one.
Once I got to the market I found everything from batteries for my camera to candied fruits. Even the pickiest shopper is bound to find something at this market.