Hi Faithful,
As Iceland is an expensive destination, I would recommend taking enough money with you (perhaps on a credit card as these are widely used, but a debit card can still be used). Prices are advertised as being like London prices so budget with this in mind; however, in Iceland some UK banks require advance notice before allowing debit or credit cards to be used in Iceland.
Icelandic Kronur are available through banks and cash machines.
I hope this helps.
Kindest Regards,
Amy