Annually, the fishing town Akranes, hosts á festival dedicated to Ireland and related Irish traditions, including Guinness drinkning. A large set of events are planned all over the town from the 2nd to the 4th of July.
Akranes is about one hours drive from Reykjavík so itf you're planning a trip over the country, starting that weekend or just want a change of local from Reykjavík, then its ideal for a little trip to drink and be merry.
Irish days official website