If you´re visiting Reykjavik over Christmas be prepared as many restaurants and shops close down from 24th to 26th of December as well as January 1st. So, stacking up with some food may be a good idea if you´re in town those days and you dont have anything booked. Visit Reykjavik website has collected a very useful list of restaurant´s opening hours as well as opening hours for other services, check it out below, just to be on the safe side.
Follow this link for complete list of opening hours during Christmas 2014