I've never done an audition before, but if I were to do one, I would try to find specific music that would be fitting for the position for which I am applying. Assuming it's a church, I would choose a song the congregation sings regularly and learn it as one of my pieces. I might also attend the church once just to see what kind of style they have. I would also have another song that emphasizes my strengths on the bass.
By default, I would stick to learning the groove of the song and being conservative and well-placed with fillers. I would want to show whoever interviews me that I'm about adding value to the already existing music ministry.
Whether or not I bring a keyboardist to the audition also depends on who exactly is doing the interview. The interviewer may be an experienced musician who can gauge your potential based on you playing to a track or without a track completely. Someone less experienced may need a keyboardist to help him/her "hear" the product.
