I don't stock up on chains. My experience has taught me to buy the best chain I can afford. I run XO1 chains on my Sram setup and XT on the Shimano. My wife has a Shimano 11 speed setup her Canyon Exceed as do I on my Chameleon. I run the XO1 on my Trance 29er. I have found that a better quality chain, combined with regular after ride maintenance, is the cheapest way to prolong the life of the cassette and chain ring(s).
When the GX cassette finally goes, I am thinking of switching to a Shimano 1 x 11 there as well. Cheaper than a new cassette and the shifting seems smoother.
Now brake pads, I do stock up on those.