I have a bag that someone on here made strapped to the underside of my saddle. I run tubeless but on long remote solo rides I take two tubes, puncture kit, multi-tool and co2 and it all fits in. I have had it for a couple of years and it is still going strong.
In that pic you don't run a dropper or rear suspension. So moving bits won't influence that set up. And you can't ruin you dropper by scratching the sides of it with the bag rubbing.
What are people using to carry spare tube/multi tool/tyre levers on their mountain bikes?