Creating a Horcrux, let alone seven, is incredibly dark, dark magic. Here's a good rule to live by: If Voldemort did it, you should probably not do it.
Which is why J.K. Rowling firmly stated that she would never, ever have a Horcrux. It's an incredibly evil bit of magic a wizard or witch could do.
However, if Rowling were to have one, she would have the most British object in mind to contain part of her soul: A teabag. When asked by a fan what she would use for her Horcrux, Rowling had this to say:
Rowling has taken to her Twitter lately to answer fans' questions. From Harry Potter characters, to personal inquiries about Rowling, I enjoy being able to learn more about the Wizarding World and about the mastermind behind the creation.
Will there be a Harry Potter on Ice? Is 'Cursed Child' a prequel? Can Rowling trust and American to make tea?
All of these answers and more can be found on J.K. Rowling's Twitter.
Thank you Rowling, for creating such an incredible and imaginative world for us to constantly play in. I loved continually learning more and more about witches, wizards, and the creatures in-between. Also, thanks for being adorably British.