I do not know what to write

Everybody knows the moment when the teacher says to you: "You need to do a free writing". But you do not know what you can write. I can be thinking for more than ten minutes and I don not have any idea. And this is why I am writing this, because I have not ideas for a free writing and I need to do this writing before monday. I have already done five free writings talking about: my last summer, my next summer, my hobbie, an epic football match, a Fortnite tutorial... And, what I can do now? The answer is nothing.