Ok so I've firmed up my plans now.
Today I go in search of the supermarket to stock up on supplies (only managed a few supplies from a mini-mart).
Tomorrow (Monday) the weather is a little changeable so I'm going to spend the day walking round exploring Reykjavik.
Tuesday I'll travel north to Kirkjufellsfoss, the rain is meant to be a lot further north plus there's lots of coast to admire on the way.
Wednesday I'll travel east to Solheimasandur Plane Wreck, the weather is meant to be a lot clearer that day.
Thursday will be the hardest day travel wise, Jökulsárlón & Dimond Beach. It's about a 5 hour drive each way so I'll be leaving early in the morning, dawn isn't until 8.45am here with sunset at around 5.30pm.
That leaves me Friday to recover & edit my photos.