Your luggage should include some light clothes, items you can layer (that way you can add or remove layers depending on temperature), at least one warm jumper, waterproof coat and/or umbrella and comfortable walking shoes/boots/trainers.
If you go during the winter, you will need an overcoat, scarf, gloves and warm shoes/boots.
In autumn and spring, you may want to bring waterproof trousers and boots.
For the summer, lighten up, but remember that even summer evenings and nights can be chilly, particularly in the mountains.
The weather forecast for Norway for the next four days.