[Taera]

Practicaly the sitting-there-doing-nothing thing with using little supplies can be explained quite good. Normal creature requiements (living quarters / life supports) requie so little supplies compared to a ship engine or a missile you wouldnt notice. You can also think of a built-in mini generator that performs all this for you or an energy recyle system.

Sensors and machinery requie electricity, which is again a minor supply usage compared to engines and weapons and shields.