Whats the use of having a lot of gold, when no one buys it?
Is it just to have a stable currency in the case when the value of money drops (inflation)?
Gold is used to hedge inflation and currency risk. Really most commodities can serve this function, gold just happens to be the most popular one. People have an affinity to gold because the dollar used to be specifically backed by, and directly exchangeable for, gold. Similarly, if you wanted to choose a different commodity to serve as your currency/inflation hedge, gold is easy to store and won't go bad. It would be hard to hedge your assets with grains because those go bad, or highly utilized commodities like steel or oil because of various market demands. Of commodities, gold is relatively stable.
I agree with you, that people holding gold to be prepared for the zombie apocalypse have underestimated the other far more immediately pressing problems that would exist if you had to shave off bits of gold to pay for toilet paper.