I always take 2 basses with me, in a double gig bag. I used to switch sometimes (and still do, rarely), but now it's there just in case. They're both very similar (35" scale, neck-thru, EMG pickups, active preamp), so it becomes a matter of which one sounds/ feels best at a particular venue. Most places we play aren't anywhere near a music store, and we normally start around 10pm, so even if there was a store close, they'd be closed. Our set moves so quickly, and has so little down time, that anything that goes wrong can cause a major hiccup. I've had things go wrong in the past- dead battery in a bass, bad cable on my pedalboard, fried amp, but I've been able to diagnose and work around most everything in a matter of a few minutes, max. Hell, I even had to solder my guitarist's output jack, mid-gig once. Was only down about 15-20 minutes, and the singers and keyboard player kept the gig going.
Unfortunately, I seem to be the only one that comes completely prepared to the gigs, and that has turned into everyone counting on me to be the MacGuyver of the group, fixing things, making things work, etc. I literally carry a backpack full of tools and supplies, and use them almost every gig. I try to keep backups of anything that can break or go bad so that the show doesn't suffer.
tl;dr- yup, I bring 2 basses with me.