You could mention a really good grade you got for a module or paper, any sports you’ve been involved in even if it was something like ‘Cancer Walk’ to raise awareness, learning a language or an instrument, art etc… Basically extra curricular activities are things that you have a genuine interest in and they don’t necessarily have to be academic. It’s a great way to show how you developed certain skills for e.g I love baking and I explain how baking involves a lot of precision and the need to be meticulous because too much flour or lack of it could result in a total failure. A future trainee would definitely need to show a great attention to detail and precision when drafting and going over documents.
An achievement could be something you struggled with for e.g a module but then ended up getting good grades. Also mentoring or tutoring a student, setting up a blog or website. In a previous job I succeeded in convincing an international clothing brand to partner with us and I consider that to be a great achievement.