I looked at it in the following way after confirming with the insurance company what sort of items you needed to take into consideration.
I thought of it as if the house went on fire and everything was destroyed inside. It's not just the furniture and white goods but carpets curtains, bed linan, duvets, pillows, not just the kitchen itself but whats in the cupboards. Think of all the clothes in your wardrobes. CD's, DVDs, computers etc,
We accumulate all these things over time so to spend 20 euro here and there on a CD or 100 euro on a pair of jeans or shoes or whatever. But if everything was destroyed and you had to go out and replace it all or even just most of it, it can add up.
My estimate came to about 20% of the value of my house.