On day one you'll arrive in Kiruna and the first stop is to pick up groceries in town. Since you'll be staying in a cabin, buy some food that will be easy to cook for breakfast and dinner. Onsite at the cabin, you'll have access to a kitchen as well as a grill.
Next, you'll head to Camp Alta to check in. The first day is just about getting settled into the cabin and enjoying the site. If you'd like to rent outdoor gear from the campsite, this is the time to do it. Once you're settled in, you can enjoy amenities - including the floating sauna and an ice bath.
If you'd like to make planning your trip a bit easier, I have also included a tour company that can book a all-inclusive customizable trip for you in my recommendations.