I do recommend Le Bon Marche for food - you can get all sorts of things from one place, and quite reasonably priced. There are also some good bakeries nearby.

I literally filled my suitcase with food on my December trip to Paris, and I intend to do it again in a few days.

Another thing I'd like to recommend is the cosmetics from Printemps, especially very 'French' ones that haven't reached overseas yet. They are on the 2nd floor of the Maison building.

Also, visit Guerlain. They stock more unusual perfumes from their range.