Many people will use registrations for gigging. That way everything in the set up can be stored against the title. However, if you start to get into multiple registrations to change the set up for different parts of the song, then you also need to mark up the music in some way so you know when to change, and what is happening. Typically gig musicians will organize their registrations in some easy to find way, - alphabetic, genres, tempos whatever works best for them.
There are other ways, which some prefer. For example some musicians like to store favorite voices and styles in a permanent set of registrations which they label on the keyboard and can call up for a wide range of songs. This suits people who don't like to get too structured. Its also possible to use the old MusicFinder and the new equivalents. That is one of the beauties of the arranger, there is nearly always more than one way, and what you have to do is find out all the possibilities and what works for you.
As far as music is concerned, some people probably still use paper, usually in a ring binder with all their repertoire in it. That is how ai always worked in my gig days, and still like that. I played a gig a short time ago and the vocalist still preferred that old fashioned way - and honestly so do I.
A small point about reading music that Gary alluded to. Most gig musicians I worked with had some kind of cheat sheet around, with lyrics and maybe chords. But they only are there as a crutch/memory jogger, and I never played with a single pro musician that actually needed to read music as a matter off course while live playing. I think its pretty difficult to be an effective and relaxed entertainer linked into your audience if you are having to read every note. It might be OK in an orchestra,or big band, but not a small group or OMB.
Mike