Don't do Philosophy. That's my advice. I've looked at some A level Philosophy specs and they don't look very rigorous, and I don't think it would help really. It certainly wouldn't advantage an application any more than reading a couple of philosophy books would.
Econ. and politics are a bit better, though neither's necessary. Maths, although not a must, is VERY helpful, as lots of people struggle with the maths in econ., even if they did A level. History is well-respected, as is English lit. (NOT language, as somebody above pointed out, though the joint lit. and lang. course isn't too bad). I don't want to be prescriptive, because you really should do subjects you find interesting, rather than picking for the course, but if you know you want to do PPE then maths and history are your best bets, and are really good for any course anyway.