The only things are to run and hide. AKA "Cover and concealment."
I know this sounds overly simple minded and was joked about in the famous Monty Python bit "How not to be seen" but it doesn't make it any less true or effective.

This was the only option on the island and the survivors all apparently survived this way, including in at least one case, by playing dead.

My heart and prayers goes out to the parents and families and to the people of Norway.