Well you do maths english and science as standard anway. But i would pick geography and history.
Geography - As stated above, maps, weather, general world knowledge (MEDC's, LEDC's etc)
History - This subject really improved my spelling, grammar, punctuation and way to put across a point. The subject is essay based most of the time so you need these skills to get a good grade, and i believe that having these skills will enable you to write a good CV and express yourself effectively.
I think the choice you get is something like geography, history, music, drama (some other pointless subjects)
Doesnt take a rocket scientist to work out what is best for any career let alone an aviation one. Unless you want to become a actor or musician i think its a bit obvious.