The Premasiri Mini Mart is a good option for a quick stop, especially since it's located right next to a fuel station.
The Food City Express branches are generally quite small but they have all your essentials.
This is located in the basement of the Havelock City premises, it's quite small but it has all the essentials.
Branas is a supermarket on the third floor of the Kollupitiya Market building - it's quite similar to Beemas next to it - it's got a whole load of imported stuff from mostly Australia, Dubai and Italy
Beemas is a supermarket on the third floor of the Kollupitiya Market building -- it's got a whole bunch of awesome imported quality goodies like Hershey's syrup, Hag's espresso, Hellman's mayonnaise and…