Blooming eck Hensen, you have half the country wondering what the heck you are wanting to bring.
You do realise that you have to let us all know after the event what the valuable item is, otherwise we'll all be having sleepless nights wondering what it can be!
We stayed at the Rila two weeks ago. We personally had a safe, however, I heard a guy complaining one morning that his camera had been taken off of his bed. A lad in our ski group had his wallet and phone stolen and the four guy in the room oposite our had four pairs of skis taken from outside the room door, so just be on your guard and if you treasure it lock it away.