Economics
Maths is a MUST here, in order to be even a lil bit competitive, you should probably take Maths, the top of the top may take Further Maths, but only really if you're aiming for something like LSE, additionally, obviously, Economics is good.
Medicine
Just Biology and Chemistry really
Together, what would make you good for both would be something like:
-Maths, Biology, Chemistry, Economics
-Maths, Further Maths, Biology, Chemistry
In Further Maths, some schools may put you on Accelerated Maths, where you do AS and A2 Maths in 1 year, however this differs and depends, your school may teach both subjects in parallel.