At Rowancroft there are Rowancroft Court, Rowancroft Mews, Rowancroft House, and a whole new bit which, in a fit of inventiveness, I think is just called Rowancroft. Altogether it looks like there'll be more than 350 people living there this year, so first off it's not like you'll be on your lonesome, and added to that and it's a safe bet that quite a few of them will be studying at the Streatham campus too.
And, like grape said, there are local shops and takeaways - literally just up the road there's a whole street with a Somerfield, a late-night shop at the garage, takeaways, and other shops including my favourite charity shop (I know, I know. But it is!) And, just because you aren't studying at St Luke's there's no reason you can't use the stuff there, like the bar and so on - and, actually, St Luke's is where the indoor swimming pool is, which could be handy. Plus, if you nip through the St Luke's campus you come out on Magdalen Road which is a really nice row of shops with a greengrocer, fishmonger, butcher, deli - you name it - and I definitely recommend checking them out. Especially the florentines from the deli. And the orange cake.
Is that helping on the cheering up front?