If you want a combination of every subject, I'd go for politics or law (or something similar). Even English Language/Literature which could open up doors into journalism (which seems like a perfect career if you're interested in the world). They can be quite academically intense though, so you'd have to be sure that's what you wanted to study.
Alternatively, if you're good at languages, learning a modern language can be a wonderful way of finding out about the world. The A-level syllabus is particularly focused on current affairs.
EDIT: History can be an awkward subject because you may not enjoy the A-level syllabus. Nevertheless, once you've done your A-levels and decided to study it at university, you can choose pretty much any subject you like. A lot of history A-level courses do include an element of choice if you do coursework, but still, it's probably not a good idea to commit yourself to studying 2 years of history that you won't enjoy. Saying that, you may be pleasantly surprised - I was absolutely dreading studying Charles I and Oliver Cromwell as part of A2 history but am actually really enjoying it!!