Ive not applied for S&S but every firm has this question and Grad Rec covered it at a few open days ive been to:
I usually structure these in a pretty simple way - if you've got loads of examples just pick say your top 5 that demonstrate your range. Best to have 5 really well reasoned things than list 20 things. If you've got 20 things, go for a combination that shows off the most variety and the most transferable or soft skills. This box is a really good place to put extracurriculars no matter what they are and show you're more than a study machine
For example that might be a couple of things you did in uni like societies or volunteering, or perhaps any more commercial courses you've done that didnt really 'fit' anywhere elsewhere in the application form along with any sport/hobby achievements. So imagine if you took say an Open U course in company law voluntarily over lockdown, although you couldn't put that in university education (unless you went to OU) that's an example of a type of thing a firm would be interested to see in that box.
Like Ricky said they're looking for transferable skills so it doesn't really matter what you've done as long as you can show the attributes they want, whether that's organisational/time management/communication/leadership etc. In every event Grad Rec has really emphasised they want to see elaboration: if you won a silver medal in water polo or something, although it's cool you did that, they want to see how it can apply to being a solicitor: did it give you discipline/work ethic/resilience, etc. Hope this helped