Pilot, co-pilot, engineer & assistant, scientist & assistant, medical support.
The issue is more why the characters don't get to perform in their logically assigned roles. Spock does the flying. Mears doesn't have anything useful to add beyond switching on the tricorder, which anybody could have done. With Rand, there was a kernel of an idea that she had some skill at improvising in a crisis that could really have been fun, so it could have been her that suggested draining the phasers to fuel the shuttle. Mears was just generic filler. I think there could have been better interplay if the characters' specialties had been brought more into the story. Of course, Scotty rocked as ever, albeit he had sufficient rank to dress down the others who were giving Spock a hard time and didn't do so.