Money is trust. And that's all it is. When you exchange a tangible good or a service against "money", it is only because you trust that you'll be able to exchange it again for different goods or services. The stuff that is used for money as no intrinsic value if that trust goes away. Be it gold. Gold is pretty useless unless you find someone that is willing to accept it for payment. Even for jewellery. Who are you going to impress with a watch made of a worthless metal? It might as well just show the time.
So, really, it is trust that we are trading, when money is going around.