I always bring at least two, but depending which band I play with/what kind of gig it is I normally use one or two on stage.
One of the bands is an old-school blues-rock band where I tend to only use my Fender Jazz strung with flats, though I normally carry my Rick 4001 or my other Jazz as a spare.
The second band I play in, I always use at least two basses on stage, because the music (which is original and not cover) needs a variety of different sounds. There I still use the jazz for most songs, though the Rick gets at least three songs, two of them with a pick, and the last with fingers.
My third band is a part cover part original music (in the sense that we've taken some known hard rock songs and mixed them with what we in Denmark call "Dansk-top" which is what the elderly usually listen to) and I tend to bring whatever bass I think deserves stagetime. Typically I will play one set with my Jazz and the next set with my 4001 or the other way around.
The rest of the smaller projects where we only play a few songs in small gigs or in the studio I use whichever bass fits the song. I did a record with the above mentioned band number two, where I used 5 different basses on 7 songs, and I only played on 6 of the songs
