I have a Steinberger Spirit that lives in the trunk of my car. It’s so small (and nondescript, in its black cloth bag) that it’s practically unnoticeable, and certainly no magnet for thieves.
It’s good for three things:
A backup bass. I don’t have to remember to bring one, or keep an eye on it, or load it in and out.
A spontaneous bass. Sometimes playing opportunities arise when I don’t have the logistical option of bringing an instrument beforehand: impromptu jams, dropping by an open mic, etc.
A practice bass. I tossed an old iRig and a set of folding headphones into the bag, making it completely up for practice sessions anywhere—traveling, stuck in traffic, staying at a friend’s, etc. Zero excuses not to practice!
Yeah, it’s a cheap Steinberger, but that still means it’s a neck-through that stays stable through temperature changes, and no protruding parts to bang up. I’ve forgotten about it for more than six months, then pulled it out and found only a few strings fractionally out of tune. Passive pickups, so no batteries to go bad.
You can pick them up for under $300 on eBay. Totally worth it, both in unmissed opportunities and in peace of mind.