Well, Im not sure, if you need a high speed internet connection or not, during your epic roadtrips, but for me, internet is everything, as I have to edit, upload and then sleep at the end of every night. Since Im heading to Iceland this september, I just finished my part of research about which 4G LTE Service provider to use and how to get a sim card easily in Iceland entry airport of KEF, and here are the best options I found :
You can get a Simmin SIM Card with 50GB of data for just 4600ISK = 3000INR just when you arrive, next to the baggage claim area.
Vodafone is another big service provider in Iceland, but they donot have a counter in the airport arrival and the 50GB sim card with internet which costs 5500ISK=3500INR.
Nova is the 2nd largest provider in Iceland, and you can get 50GB sim card with internet which costs 5900ISK=4000INR.
BLUE-CAR RENTAL 4G WiFi Addon
If you are renting a car, I highly recommend getting it from Blue Car Rental. I have read a lot of good things about them and all of my friends, suggest the same too.
You may go an unlimited 4G WiFi addon from them for 900ISK=550INR only.