Oh my- where to start!
I go to Paris a lot and my list of things to bring home keeps getting longer and longer.
For clothes, my favorite store is COS, which is not actually French, but Swedish. I love almost everything they have! For shoes I always seem to have good luck at Minelli.
Don't miss Galeries Lafayette department store, if only to gawk at the gorgeous stained glass dome and to go up to the rooftop observation deck for a great view of the city. It's a madhouse, but a great place for one-stop shopping.
I bring back lots of stuff from the grocery- Monoprix is great and has locations all over. Herbal teas -my favorite is Verveine Menthe flavor, Maille mustard, Harissa, Piment d'Espelette, the most wonderful basil and thyme-scented liquid dish soap by Maison Verte, cheap store-brand shampoos with nice scents.
The Grand Epicerie food hall at the Bon Marché department store is so much fun for browsing and to find all sorts of food goodies.
From the pharmacy: Caudalie shower gel, also Roger & Gallet shower gels and hand soaps. Voltaren gel to apply for aches and pains, La Roche-Posay sunscreen.