Bring your own drinks at a party
Alcohol is significantly expensive in Finland. Many Finns throw parties in such a way that every guest has to come with his/her drinks.
This type of party is always indicated on invitation cards. If you see OPM ("Oma Pullo Mukaan") on your invitation, then it merely means bring your bottle.
However, this is not the case for every party. Some do offer alcohol and other drinks.