The Cité has a long row of souvenir shops — the better ones sell wooden swords and replica medieval pottery; the worse ones sell plastic. Avoid the "magnet street" near the Porte Narbonnaise unless that is what you came for.
Down in the Bastide, rue Georges Clemenceau is the main shopping street. The Tuesday/Thursday/Saturday market at place Carnot is the place for cheese, charcuterie, and the white beans for cassoulet. A larger producers' market sets up at Halles Centrale most mornings.