I'd recycle them and move on.
Unless my first glance at something like this sends a creative message....'Hey! I could make that into a _______ for the layout!!!'....collecting/saving things like this is what creates the junk piles in the house.
You know those little coffee creamer cups with the peel-off tops?......they make dandy trash cans in larger scales (not my idea, someone else's.) After saving just short of a bazillion of these, it suddenly dawned on me that they were pure trash themselves!.....and so they found a new home in the recycling container placed at the end of the driveway one day.
So, the other thing I've learned in life....if I received that first-glance creative message above...is that if I don't actually create that gizmo within a week or two, it will become this nuisance thingy that clutters my life....to the point that years later I'll see it on/under the workbench and say...."What the %#@$& am I keeping this thing for??!!".....inspiration long gone. THEN it ends up where it probably should've ended up long ago!
I know, that's not what you wanted to hear re these spent cartridges... Sooooo....
You could cut them in half....pitch the narrow ends. Then paint the domed ends bright yellow, put some faces/hair fuzz on them, pack them into a gondola or behind the opening door of a boxcar, and....Voila!....MINIONS!!
Well.....you asked.
More coffee please......
KD (Lucas Gudinov)