The Central 1 Card is a discount/loyalty card. There’s one for tourists and one for residents. Sign up online, at Central’s customer service desk on the 6th floor or at Thai Watsadu’s customer service desk, among other locations.
You’ll need your passport to sign up. Discounts start at 5% and are available at Central Department Store and many of the other stores found in Central’s malls including the one closest to Nichada.