I would like to add a couple of things to the list.

Kaffi Loki in Reykjavik, right across from The Church, sells black bread ice cream. This sounds absolutely not something anyone would like.

It is absolutely fantastic. Basically, the bread adds this wonderfully crunchy texture to just delicious ice cream.

They also sell a traditional Icelandic herbal tea which is worth trying, just don't think too hard about the fact that it has moss in it. It's not something everyone would like but it had me coming back for seconds!