I just spent the vast majority of my PS writing about the books I'd read. Also if you go on the open university website there's free mini courses you can do, it's mostly just slideshows and only takes a couple hours but you can massively big it ip in your PS. And if your college ever has essay competitions or guest speakers then you can talk about stuff like that as well.
I think on mine I had about 3 or 4 books I'd read, one open university course, a translation competition I'd entered (I do law with French law) and didn't even win lmao, my entry was just commended, my EPQ and a tiny paragraph at the bottom that they forced me to write about my hobbies and non-law related stuff, and that was it.