I like the idea! I use a bench top grinder, the Oregon 620, and because of that, I never sharpen using files on the bar out in the woods anymore.
My dull chains go into an old metal coffee can, the sharp ones goes onto a nail hanging near the grinder.
My property is small enough that when I go out cutting, if I need to swap chains, I just go back to the shop and do it on my work bench. However, carrying a spare chain is something I've done from time to time. Never thought about using a locker. I just pile it up on the floor board of my tractor with the wedges and wrench.
Yep I'm curious how folks bring spare sharpened chains into the field besides just putting them loosely in an old ammo can or satchel. Over the years (until recently) due to my stubbornness on taking the time to learn to sharpen chains I've acquired a large collection. Now most are sharpened pretty well and I'm trying to devise a good way to transport spare sharpened chains in the woods.
I save the cardboard boxes that new chains come in. They may need duck tape or relabeling with a black marker but they last a long time. I put the boxes in a small tool box that I take with me into the woods.