Hey, I'm at the slade now. I know how melted your brains must be from the whole application/portfolio stuff so hope I can help a bit.
In your portfolio, they don't necessarily expect anything from you. I'd include works that you feel are your strongest and would feel most confident talking about if you got an interview. It's good to see the spectrum of your work and how all the different pieces have some relevance to each other. I can't stress enough how important it is to photograph 3D/installations/sculptures/larger pieces in good lighting and documented well from a few different angles. Always include their dimensions if you're showing documented work. Stuff that is still in progress and unfinished shouldn't be ruled out; it gives you an avenue to talk about how you work and show the tutors your stages of development. If you work in sketchbooks and they're relevant, then put them in. I photographed a few significant double-pages of my sketchbooks and put them in, and put one or two a4 ones in too. Don't be tempted to pad out your portfolio with 'fillers'. By this I mean don't just put 'average' work in for the sake of bulking it up; there is just no point. I had a few sketches and plans of early stages of work, can't say whether they "like" this or not but as I said before, it just shows how you work as an artist. Just a heads up, every year the tutors comment on the amount of Jenny Saville-style work people put in their portfolios. I guess it's not necessarily a bad thing, but they do see lots of it.
So yeah, you can ask me other stuff, not sure if i'll be much help but i'll try! Good luck everyone who's applying and i'll maybe see a couple of you there next year!