In Trek, we have encounter many "civilians". But upon further reflection, many of these menial occupations simply make no sense.
Servers on Ten-Forward:
Why would you need such people? I get that you need a dining area but couldn't people just bus their own food from replicators?. Or just have non-sentient robots do it! And in Trek, since no one seems to have to work to survive, why would anyone want such a menial job anyway?
Boothby the groundskeeper:
Really? I mean IRL this is a menial job that people do to survive. Aren't there robots or fully automated grounds keeping equipment that can do all this work?
Joseph Sisko, restaurateur
In the future where all food can be prepared to perfection with replicators at home, the idea of someone doing all the grunt work of running a restaurant seems out of place. Maybe he runs it as a hobby and sets his hours as he sees fit?
Robert Picard, viticulturist
I suppose one could say its just a hobby rather than a true occupation. But otherwise this "occupation" makes no sense. Would seem to be completely obsolete.
There must also be a lot of people who do all sorts of other grunt work, both for StarFleet and in civilian life. But why would they do it?
I am sure that I am missing a lot more examples of menial occupations that simply shouldn't exist in such a futuristic utopian Trekverse. Having said that, I can still imagine people being artists, athletes, scientists/engineers/physicians and so forth.