This is a decent idea, although a bit unrealistic for a few reasons. A real lock can be picked with a variety of objects such as bobby pins, a piece of wire, etc. in addition to a conventional lockpick, so having this magical lockpick that randomly spawns be the only way to open a lock does not make much sense, not to mention the fact that you can skip picking the lock entirely by breaking the lock off with various tools, busting the door down, breaking in through the window, and so on. The idea that the lockpick is a one time use item is also completely unrealistic because a real lockpick could potentially be used multiple times without breaking, especially in skilled hands. Like others have said, having these locked containers be the only place to acquire "premium" gear is also completely unrealistic. The reason being again, in real life, there are plenty of people who would have their weapons/ammo/etc. out and ready to defend themselves because of the, you know, zombie apocalypse that's going down, or just because they didn't bother to lock it up in the first place; the former being true for the military as well. It would be more realistic to have some unopened lockboxes/vaults, which can be picked or broken open, of course. Don't forget that some people sleep with a gun under their pillow, some people keep a rifle nearby, whatever. People even collect lockpicks, so finding multiple of them in one location would be perfectly realistic.