Most grocery stores are open Monday-Sunday, from 8am to 10pm (sometimes later). Retail shops are usually open Monday-Saturday from 10am to 8pm. On Sunday, all shops (except at train stations) are closed--which makes it a great time to check out one of the many flea markets, to kill time while also getting to know the city better! Visit the markets in Mauerpark (U-Bhf Eberswalder Strasse), Treptower Park (walk east on Köpernickerstr), and Tiergarten (S-bhf Tiergarten)
Boutique Shops line Kastanienallee (U-Bhf Eberswalder Strasse) and around Prenzlauer Berg.
The Weihnachtsmarkt (Christmas Markets) - these are in most public spaces during the holiday season.