Yeah, I think it is just those two.
Basically, unless you opt out strongly you will have to pay KFC. Although it isn't all for subsidising your college meals- some goestowards the upkeep of the gyp rooms- the largest proportion of it enables the college to have buttery meals at a cheap price. Seeing as you're paying for it, you might as well go to Buttery anyway. I found it was not only beter food than I could cook, but you got more of it. And of course it was far more sociable, seeing as pretty much everyone on my staircase went to Buttery together.