With the many flights between kastrup and keflavik for the past few years, I've made it a habit to stock up on several types of products that I can't live without (ok that was a bit overly dramatic - products that I use everyday).
What I didn't know until last year is that Kastrup airport is the place to buy M.A.C. cosmetics (the next best thing to buying them in USA). For example, their concealer (which costs around 4.000 ISK in Reykjavik) costs around 100 DKK (c.a. 2.000 ISK) in Kastrup.
Hope this will become useful for you fellow M.A.C. lovers