Spare cable wasted weight?
 

... or get one of 'em machines they have at the factory to finish the cable ends... ;)

I have 2 shift cables (Rolhoff) and 1 brake cable (MTB) slid into the stiffener of my jerry can (bikepacking bags). They pretty much live there all the time.
I've needed one once, not for my bike, but to help someone out.
I also keep the multitool, chain tool, extra quick links, spare brake pad set (discs), etc. etc. in there.

I haven't trimmed them to size, but I use heat shrink tubing on all my cable ends, once installed.

interesting how these things happen. wore out the derailleurs and cassette
and chain and chainrings, so was in the process of replacing them all for an
upcoming tour into the jungle in laos.

decided to shorten the rear derailleur cable housing to match exactly (at
least visually) the front housing.....pulled the gear cable from the shifter,
cable is dead, hanging on by three strands. pinched and ripped on the
inside of the shifter, but no affect on shifting. (rd pulleys worn to nubs
and the return spring stretched out).

old cable? nah, newly-installed by a bike shop mechanic about 500 km
ago. old cable got corroded in the mud and monsoon rains, managed to
limp into town, easier to let the mechanic do something so simple and
replace the lower housing at the same time.

well, found i'm out of spares in the apartment, so dug out the spare cable
from the touring kit........finally got to use the cable i've been carrying
around for 50,000 km!