I got four interviews for medicine and these are some of the activities I have done just to give you an idea of what helped me in my interviews:
The more things you can get done the better for sure.

Duke of Edinburgh Gold.

Worked in a team to make a workshop about mental health and resilience for year 6 students.

Worked on a project to raise money for the homeless and then I had the opportunity to speak to many people sleeping rough to give me more of a social awareness in my area.

Work experience (in person) in the theatres with an ENT surgeon and his team, in a children's hospital and an eye hospital.

I am also a subscriber to the BMJ but no questions about extra reading came up in my interviews. There weren't any appropriate times to bring them up either in any other questions so don't stress on stuff like this.

As an extracurricular activity I have done wall climbing for a few years (cycling as well).
About your running, if you can talk about running and what you have achieved/how it helps you etc then there is no reason why you cannot talk about it! There are no wrong or right answers.

I now also work as a HCA in a cardiology ward which has been a very valuable experience. If you can get a job as a HCA then do so!!!!! It can really set you apart from other candidates and prove to the interviewer that you are committed and have a good idea of what it's like working in a hospital.

I definitely missed somethings about but I cannot be asked to list them all here as I think you get a rough idea. If you can express your ideas and your answers well then you should be okay. All universities want to be sure that you are a well rounded person with a good work-life balance.