This is all really great stuff! The research papers, MUN, and summer course are great things to go into more detail about (provided that they are relevant to your interests and the course). You should highlight the skills that you have developed in doing all of the other activities.
If this is for your personal statement, the majority of it should be subject specific. Especially for Oxbridge, you should read around E&M and focus on providing a thoughtful and critical analysis of a topic that you are interested in. Some of those interests and arguments might come from those you have listed.
As a successful oxbridge applicant, my personal statement only had around two sentences on extracurriculars and the rest was academic. Of course, there is no single rule and you may be successful by taking a different approach.