As with any travel, check you exchange rates a few weeks ahead of time and be prepared! The US Dollar had done a nose dive in the weeks before my trip and it turned out to be quite a bit more expensive than I had planned.....
Reykjavik is, like the rest of Iceland, e-x-p-e-n-s-i-v-e. A few example: A meal in a bistro 14 euro, Big Mac Menu 8 euro, large beer in a bar 6 euro. It's expensive to live here and even more expensive to be a tourist. But consumer goods like clothes, electronics etc. are not expensive and you can get a 15% tax refund.
Dangers....mmmmmm that is tough because Reykavik seemed to be such a safe place! Warnings...well it is expensive! That is true! If you plan to go to a bar, it will be very expenisive . a glass of house wine or beer was about $5 or $6 US. It is a good thing I am not a big drinker!
Everyone except us headed straight for the Duty-Free on arrival at the airport. Wise move if you like alcohol, otherwise expect to pay treble UK prices.