Sichuan peppercorns are a big deal in Chongqing, so it's a must to buy a fresh bag before going home. Don't buy them pre-packaged at a generic tourist shop; instead, head to the Ciqikou neighborhood, which has an area packed with dozens of little spice and tea shops.
Shop owners normally offer you samples to try. Fresh peppercorns should still be a little chewy, not dry and powdery, and should quickly turn the inside of your mouth numb. As well as different types of peppercorns, you'll see numerous chili peppers, spices such as anise, and mixtures such as the famous "Five Spice." Buy them all to try at home or give as fantastic gifts.