You really don't have to save the whales, devise a three-state solution in the Middle East, or start a business empire. Engage in super-curricular activities which (a) you will enjoy, (b) will inform you about the law in broad terms, and (c) will communicate to universities that you have thought carefully about why you want to study law.
Reading is the easiest route. Everyone reads Tom Bingham's The Rule Of Law, but that's because everyone should read it. There are many non-technical books by and about law and lawyers - have a browse in any large book shop, especially one in or close to a university. There are also several podcasts, substacks and blogs about legal issues, by writers such as Joshua Rozenberg. Reading The Economist can be a useful way to be well-informed about political, economic, social, legal, and cultural issues.
Have a look at a essay competitions, and debating and mooting and mock trial events. These may be advertised on the websites of the Bar Council, the Inns of Court, the Law Society, and universities.
Read about hot-button issues such as law and AI, law and climate change, regulation of business, freedom of speech, trial by jury, selection of judges, and so on.