Think about power generation, and ways to improve what is already there. Aircraft are getting more power hungry, so what can be done to mitigate that - schedule loading to spread demands across the flight perhaps?
Anti-icing comsumes a huge amount of power. Can you think of a different way of achieving it?
Is there a better way of controlling flight than sticking panels into the airstream? Ducted air perhaps?
In flight entertainment is a huge part of the passenger experience, and is drawing more power & resources with each new aircraft. Can it be optimised to reduce hardware, use less power and yet give passengers a better opinion of the operator?
Cooling electronics is the next major hurdle for aircraft. Can you develop a system which does not raise the drag penalty and is able to dissipate all the heat generated onboard?
There's a few for you!