It really doesn't matter what the extracurricular activity is - what you need to demonstrate from the extracurriculars you do are commitment/dedication, having impact within them and transferable skills gained. But whether it is sports, arts, volunteering, faith/politics, academic/intellectual, community-led, or something just fun, it really doesn't matter - I have seen ultimate frisbee and cheerleading to be as (and sometimes more) impressive as "traditional" extracurriculars like mooting and writing for legal journals.
You definitely don't need a summer internship in banking, consulting or financial services. If anything such roles could bring into question why you want a career in law. It is not that they should be avoided, but they aren't going to automatically make your application stronger.
It doesn't matter if your work experience is in the UK or not. However, if your experience is predominately outside of the UK, I would recommend weaving in "why commercial law in the UK specifically" into your motivational answers in applications and interviews.
You don't need anything unique at the same time. Lots of people have very "traditional" profiles that are very similar from candidate to candidate. Its really about highlighting your individual impact and success in your activities as this is what makes you unique.
