What is a topic you think you can speak about for 30 minutes without any preparation? What truly engages you in a way that you can simply choose to speak about it on an impulse and maintain a nice, rich conversation about it for a good half-hour?
Doing some introspection about what these topics are to you and deliberately working on them can constitute a good exercise in developing your own self-confidence and broadening your horizons:
you will know where your genuine interests lie;
you can further expand on topics you already like, which can enable you to discover new related topics that you wouldn't otherwise know about;
you will know more about these topics than the average person which makes them good topics for ice-breaker chats and social occasions;
Diversify your own interests
Once you have done some self-reflection, you will be able to identify a few topics (say 2 - 5) on which you can speak without preparation. This essentially gives you a lot to talk about and each topic can be seen as an avenue from which all other conversational topics can emerge, so, in essence, they are like hooks for you to steer your conversations towards topics you want.
Here's a tip to grow in terms of your culture and expanding your own horizons:
Diversify the style and thematic of the topics you can discuss at length off-handedly
By doing this, you will force yourself to leave your comfort zone and will be able to grow as a person since you will discover new interests and shape yourself in the process of learning more about them.
Conclusion
By focusing on topics you are knowledgeable about and interested in, you can find adjacent topics that can allow you to broaden your horizons and become a more well-rounded person with more to offer when it comes to having and maintaining meaningful and engaging conversations.