There are several supermarkets around Helsinki that are open till late at night, seven days a week. So far there hasn't been any though where you could really go any time.
But now there is one. Siwa was clever enough to open the first 24/7 supermarket. And it's not anywhere but located right in the city center on Esplanadi. So no matter what time you leave the bar, club or pub you can still by your groceries for the next days. A genius idea. Check it out!