Supercurriculars

how important are supercurriculars on a scale of 1-10?(especially for lse)

Well put it this way. 20-25% of students get As and A*s or 7-9 at GCSE. That is a quarter of any cohort. So when you are hit with a 1000 applications all with 3 A*s, how would you start picking and choosing?
As for employers - extra curricular are worth more than a degree. A degree says you are good a sitting exams and writing essays, two skills pretty much no employer is looking for. Extra curricular sees you developing team working, communications, leadership, organisation, self-management and all the skills employers are actually looking for.