My tip for your statement- structure it in the vein of "This entry - level book/experience/job developed my interest in a particular area of econ, so I read this book on it. This is what it made me question (show that you've engaged with the ideas in the book, not just that you've read it) . These books then led me to go read this article..." etc. My extracurriculars worked well with development economics, so i researched into that. I then followed the paper trail (by writing about metrics of prosperity I'd read about) into econometrics. For you, you could link your experience volunteering for your corporate responsibility charity, say it made you realise the importance of sustainable economics in general and not just locally, and then say it led you to go read those books. And if those books are ones everyone is likely to have read, go read more. The most important thing is that you demonstrate your passion for the subject by showing you've engaged with it of your own volition, not telling them you're passionate about it. And if you're really struggling, write the start first. Also , you don't need that many flashy extracurriculars to be competitive - they don't matter as much as showing you've really engaged with the subject. What you've done so far sounds great.