There's a few that really should be made more important than is often the case:
1) Battery Guy (or Battery Girl, as appropriate), for reasons already mentioned.
2) Media rep. Three robots since, I'd kill for any videos or pictures of my rookie year robot.
3) Marketing, in nearly any sense of the word. (A subset of this would be any degree of graphic design. Just applying a little bit of aesthetic design work to your signs, shirts, and robot can make a world of difference. I think we can all agree that
this looks much better than
this--and that took about an hour and a half and $16.25 at USC's computer lab.)
4) The role dubbed by the kids when I was on 1293 "Rules Nazi". I think the politically correct phrase is Compliance Officer, but that's more syllables. Having one guy who internalizes the whole manual and makes sure the robot is within the rules (even if it means irritating the rest of the team to the brink of insanity) is a lovely thing come inspection time.