I’ll also give you a list of things you should definitely not leave at home, because it could be expensive here.
Waterproof clothing and shoes. Iceland is totally unpredictable. My mobile phone broke down the first week, because it just didn’t last even in a waterproof jacket. Think of warm shoes that will not get wet and in which you will be able to march.
Thermal underwear and wool socks. The temperature sometimes seems cool even in winter, but when the wind leans against you, you will feel that it is from 10 degrees less. Don’t underestimate the bottom layer and wear sheep’s wool perfectly.
Good camera and tripod. Iceland is worth a beautiful photo. You will often not capture what is really here on your mobile. And especially the aurora borealis! You won’t be able to take a picture of it without a tripod.
Airport bottle. If you like to drink something sharper, I would recommend you to buy a bottle at Duty Free at the airport, because it won’t be cheaper in Iceland.
Driving license. You never know when it will come in handy in Iceland. Traveling by car is definitely the most comfortable option.
Map or guide. Don’t underestimate the preparation. When you stand on a deserted plain and freeze your hands on the map to see if you have gone astray, you will regret it. Before each trip, take a look at the weather, the availability of the route (Road.is application) that you have planned and let someone know where you are going. If you don’t have friends, you can use the Safetravel application, for example.