Hey guys
I'm having my first gig next saturday

hyper

and both guitarists will be bringing a back up guitar. It's gonna be a very small gig (we're the opening act so we're only going to play a 30 minute set, in front of 150 - 200ish people). Is it necessary to bring a back up bass, or should I just bring my main? I have no problem with my back up bass, I just don't really fancy bringing 2 basses if I don't need both of them.
If you maintain your main bass properly, the chances of having a problem with it are very small. But there is always a chance.
What I do is balance 1) how much of a pain is it to carry an extra bass, with 2) how important is it that the gig goes smoothly without interruptions.
You take your chances.
Personally, I very rarely take two basses, and only if I space is not a problem etc. I keep my bass in perfect condition at all times, I use it a lot. My main bass is a Stingray, so despite having installed a bypass switch, I still make sure the battery is not going to die on me by replacing it before it fails.
I have spare batteries, and strings, and a string cutter with me.
I have a spare strap, and duct tape in my bag always. I have a spare cable too. Those things don't take up much space. If I broke a string (seriously, how often you get that? most people don't get that ever in their playing lifetime) I can change it in a couple of minutes while the band jams something without me.
In most situations even that would not be considered a problem. Of course, it is very different if you are in the orchestra pit of a play... but for your standard gig, even weddings etc... replacing one string is not much of a disruption.
Nice to have a spare bass, but its importance is, in my opinion, vastly over-rated for 95% of the players here.
I'd be more interested in having a DI box of some sort handy in case my amp dies. And I do have that with me in my pedalboard.