I'm in the same position as you, at the moment
I couldn't really bear to drop more than one subject - I took maths, F-maths (planning on dropping), physics, chemistry and english. My school's really supportive - quite a few people take five ASs, then drop.Some have dropped more than one AS - planning on taking 3 A2s, others are going the full way and taking five A2s . . . I don't think I'll go that far
I guess I could afford the time because I did a load of chemistry lab/hospital work placements during summer of yr 11 and I've volunteered at a hospice for a while. It's whatever works for you - some of my friends are using the free periods they get to bulk up personal statements, but I thought I had enough stuff. Pretty sure it says on the Oxford and Cambridge websites that they put more weight on the interview, as they don't consider personal statements to always be a accurate representation . . .
http://www.applytocambridge.com/applying/faqs/I'm currently not sure whether to go for natural sciences or medicine though, what about you?