I look forward to arriving or switching trains at the Gare Centrale, just so I can stop and buy pastries here. There is always a long line but it is completely worth it. At Christmas they sell these mini bûches de Noël with chocolate ganache, pear, raspberry, caramel, and hazelnut flavours. They are so rich and delicious that I usually don't get around to saving the cakes for my friends and family back home. Their almond croissants and pains au chocolat are mouthwatering, as are their small tiger-eye hazelnut cakes.
Surprisingly, their savory selection is just as good. We had an amazing vegetarian sandwich with some kind of flavourful smoky lentil mushroom pâté on nutty crusty bread. It was so unexpectedly good that when we got back from our destination, we went back for seconds (but unfortunately the sandwich was not featured that day). They also sell spreads, local cheeses and other gourmet items here.
By the way, I've been to another location in Marché Atwater which I remember being just as consistently great. Bottom line: do not miss this place if you're ever in the vicinity of the downtown train station!