Many meals come with some sort of potatoes (sometimes two!): mashed, boiled, fried or baked, sometimes with some other root vegetables thrown in for variety.
Finland is known for its many lakes and rivers, which means that fresh fish are a popular Finnish food staple here, even in the winter time when ice-fishing is a popular past time.
Reindeer is a major diet staple in Finland. Very little of the reindeer meat is exported, it’s nearly all eaten domestically, in a variety of creative ways and is a staple in Finnish food.
Most Finish bread is dark rye bread – dry and sour. You can find rye bread at nearly every meal and rye crisps are a popular snack.
Lapland is known for its vast variety of berries, which by law belong to anyone who wants them. Raspberries, cranberries, strawberries, bilberries (similar to blueberries), lingonberries, cloudberries, crowberries and more.
Like all of those far northern European countries, Finland distills vodka- sometimes in flavors like raspberry and cloudberry and it is definitely a staple Finnish food (or liquid).
Chocolate is a major Finnish food. The market is dominated by Karl Fazer, which produces 65 million kilos of chocolate a year in a huge range of flavors (strawberry yogurt, honey, cloudberry etc.).