My spares kit, when touring on a derailleur bike, includes a down tube friction shifter with a cable attached. It's the size of a matchbox, 70g, can be fitted front or back in less time than it takes to fix a puncture and leaves me free to use my shifters of choice (Ergo 9spd) without worrying about mishaps.
I started carrying it after crash damaging an Ergo about 15 years ago, I haven't used it yet.