For batteries, cigarettes, snacks, chewing gum, magazines, dairy products, refreshments, and much more, look for the small kiosks (“periptera”) that can be found practically everywhere. There you will find everything you need. The big kiosks, located mostly downtown around the squares of Syntagma, Omonia and Kolonaki, usually stay open all night and also sell international press, tourist guides and more.
Tip: If you are lost, ask the owner of the kiosk for instructions. They usually speak English and can help you find your way.