Just don't do it!
Instead, of wondering what should I talk about, ask what do they need.
It's a better approach and immediately starts helping you relax. With this approach you are not the focus, your audience is.
Don't hunt for a topic. Decide what you want your audience to do. Your audience may be a client, a prospect, a group of fellow employees, your club, the city council whoever you talk to. What do you want them to do differently after your talk?
Gather the information they will need, then design, deliver and interpret that information in a way that will lead your audience to action. This way your focus is on the audience.