I'm currently in year 12 - you will find that once you get to Sixth Form (assuming yours is similar to mine) you'll start thinking about university even more than you have been pretty quickly. In year 11, it felt like I had all the time in the world before university but now it seems ominously close. I found myself doing a lot of research in to universities from almost the start of the academic year so I've got the beginnings of a plan now.
You only need to take a brief look through some more advanced physics textbooks (undergraduate level) or watch some university lectures to see the difference between the physics you'll be doing at university to what you do at GCSE and A-level.
In the UK, I'm pretty sure that I'll apply to Cambridge and Imperial and then three more modest choices - I'll need to attend some open days before making decisions on these. I am also considering applying to some universities in the USA; MIT and Caltech both have excellent physics faculties but taking SAT tests and filling in all of the forms seems like quite a big effort, especially considering that international students' chances of getting in to MIT are very slim at best. Still, it's probably better to give it a go that to never know.
My AS-level options were physics, chemistry, maths and further maths. The way further maths is timetabled at my school means that I can carry all four on to A2 level.
Being as you're considering similar options to me, I might as well tell you a little bit about them. They all seem to compliment each other really well. As I said before though, physics so far has been rather trivial and looking through the AQA textbook, it doesn't look like it will be getting much more interesting anytime soon. Mechanics modules from maths should help you with some of your physics. Not many people seem to find statistics too hard but S1 (OCR) isn't terribly interesting.
Once you have learned at least the basics of calculus, you will find that a whole new world of physics has been opened up to you - a lot of the interesting stuff requires some knowledge of calculus, however small. This puts it out of reach for a lot of year 11 pupils. Particle physics is a good thing to be interested in; not only can it take you right to the cutting edge of physics but it doesn't have to be too mathematically intensive until you want it to be. As for M-Theory and a lot of modern physics, I wouldn't believe anyone who said they fully understood it. Down at that level, everying is so small it's practically impossible to visualise it, making it difficult to understand. Of course, that is part of the beauty of the forefront of physics as well. I personally don't think M-theory is quite "there" yet but something similar or a development of it certainly has the potential to sort out a lot of our theoretical problems.
I have just finished reading Einstein's "Relativity - The Special and The General Theory" and I will probably continue looking at relativity for a couple of weeks before looking at quantum mechanics again (I have just ordered a copy of Paul Dirac's lectures on quantum mechanics from Amazon).
After you have started AS maths and physics, I would recommend that you try to find a cheap copy of Resnick and Halliday's "Fundamentals of Physics" or even just the problem supplement to it in addition to your board-specific textbook. Whilst it is criticised by serious physicists for being too basic, it seems to tie in well with the AS physics and the mechanics modules for maths. You can solve a lot of the problems just with the knowledge you will gain in school, they just require a bit more thought. Some will require you to do some further reading so it represents a good balance between accessibility and a challenging level of difficulty for AS students interested in physics.
Sorry for the essay of a post