You can do your dishes in the river
If you planning hiking (in summer), not too heavy staff, it is nice to feel light and you usually do not need to carry water with you.
Good shoes is a must, even in the summer you will need a good jacket as it getting very cold at night, it has happened that our toothpaste was just about freezing in the morning. Also recommending a thick leather jacket or so, that the mosquitoes cannot bite through because they will get through your normal cloths, jeans and wind jackets.
In the local stores and gas station you can buy mosquitoes repellent etc. You will surely need it in the summer and just for the information, the mosquitoes here are twice the size of mosquitoes which are for instance in the southern Europe region.
What ever you have, take with you. You will never regret it. Don't plan to buy additional items in Finland, they cost more here, but films are rather cheap. Buy the films...