Lord, have I ever broken a lot of strings. The first REALLY BAD one was when I was 17-18 years old. My high school rock band was play at Crown Hall in Mendocino, CA. I broke one and didn't have a spare. To make things worse, I had Johny Barbata, Craig Chaquico, and Joel Scott Hill sitting on stage behind the band. I was pretty much a self-raised kid, I didn't have any parents there, no help, heck the music store probably didn't even HAVE Bass strings. So, as I was sinking in shame on the stage, Johny Barbata, who was kind of a friend of mine, from behind me, turned to Joel Scott Hill, and asked him what he did in a case like this. And Joel thought for a moment, and said, "I don't play bass, but on a guitar, I used to unravel the wind from the core of the broken end of the string. I'd expose enough core wire to rewrap it around the Ball of the String". This trick WORKED!
Years later,(early 90's), on a Sunday rehearsal night, it happened again No store open, no spares. So I did the trick again in front of the lead Guitarist. His eyes went wide open, and he exclaimed, "Mark! You just saved me a pile of money!" He always broke his guitar strings on his double-locking shred Guitar at the Bridge. From then on, he's coil his Guitar strings up by the tuners, feed the string down to the bridge and lock both sides down. When the string broke, he'd just slide more string down, and re-clamp it. He told me he's get the equivalent to SIX sets of string out of the one set! Chalk one up for Joel Scott Hill! Lol!

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I STILL have a box full of old Bass strings, I touring through Flagstaff, Santa Fe, --places that don't have Strings, and there was no internet back then, so I'd have to order strings from a Store, and they wouldn't bother unless you ordered three or more sets. Heavy gauge so they'd last longer. When one broke, I'd change all of them, and save the others in case. I bet I have 50 sets of used strings still in that Box.
I can afford to bring an extra Bass now. But the original question was two basses...but I say three! One with Flat-wounds, one with Rounds-wounds, and an Acoustic for the acoustic stuff! My main three Basses: