The weather in Iceland changes all the time but when the sun shines the is remarkably clear, so don`t forget sun protection.
Because of the very changeable weather in Iceland, it's always a good idea in summer to carry a light and preferably water-resistant jacket, and when the weather can be extremely changeable bring also warm waterproof clothing, and it of course also depending on you are doing everyday things in the city or you standing outside in the nature perhaps for looking for the Northern Lights, and in wintertime it is always a good idea to bring a lot of warm layers.
The Icelanders often say, “If you don’t like the weather, just wait 10 minutes and you’ll get something different" - and they’re not kidding.
For efficient layering, start with a base layer like a cotton tank-top or a soft wool thermal top and then add a tight, long-sleeved shirt. A fleece is a good idea if you plan to take a walk or are going hiking. The last layer could also be a cardigan or jacket and then add a scarf and you`re done.
It is also a super idea to bring a bathing suit. Icelanders’ favourite pastime year-round is outdoor swimming in the countless geothermally heated pools and lagoons, which are as warm as bathwater.
If you plan your own individual tour bring a rucksack or small backpack for your daily essentials like camera, wallet, medications, extra clothing layers or other personal items. It can also come in handy for hiking excursions or picnics.
Normally if you are travelling by one of the many guided tours or adventures from travel operators like example Nordic Visitor in Iceland, they will also guide about your dress code.
Here is an idea for an all year round packing besides what you generally pack: