I use them for other supplements.
I'm kinda a supplement fiend so my girls are getting raspberry leaves, MSM, flax seed, and loose salt(cuz I have no where that's accessible all the time and covered to put a salt block in) with their ration balancer. The only thing that actually comes in its own container out of those is the MSM. I've just reused other supplement containers so I have a flax seed "bucket", a salt bucket, and a container for the raspberry leaves.
It confuses the heck out of my lesson kids (another bonus!!) but it's more convenient than trying to use whatever awkward bag the stuff originally came in.
I also have my indoor cat's catgrass growing in another leftover container. My mom says it looks trashy, I say it looks "eco-chic".