You don’t need to carry much food with you on the St. Olavsleden trail as there are grocery stores along the way. However, you will need clothes for all types of weather.
You can sleep under a roof the entire length of the trail, but camping is sometimes a good option both for the freedom it gives, and for your wallet. For camping you then of course need a tent, sleeping bag and sleeping mat. When housing inside most places have bedding is included, or available to rent, but a light travel sheet is always nice to bring.
There are shops and restaurants along the trail where you can eat or buy food. But if you pack a camping stove you’ll have more freedom. A tips is to fill a thermos with hot water at your accommodation so you can make soup or a cup of tea or coffee during the day. Also bring a bottle to fill up with water while you’re hiking. It’s fine to drink the water from the St. Olav water sources and from running water (streams and rivers). Don’t forget to bring a sitting mat for your breaks.
Footwear is always important of course, but it is particularly so when you intend to walk something as long as the St. Olavsleden trail. Choose boots that you have already used for a while, and if you’re going to be carrying a heavy rucksack, it’s a good idea to wear hiking boots with a higher ankle for extra support. You should also pack rain clothes, warm layers – preferably wool – and a change of clothes. Since it can get pretty cold, especially in the mountain areas, a warm hat and gloves is always a good idea. It can also be lovely and warm, so bring bathing clothes and a small towel, and perhaps a pair of sandals to change into in the evening?
Other items that are good to pack
Make sure you have a map easy at hand, and perhaps a compass to orient yourself. You might want to bring a small notebook – you get the best ideas when you out hiking. A first aid kit is important. Mosquito repellent and a sitting mat are also handy. Don’t forget your chargers and toiletries too.