I can go either way, depending on what I'm looking for on any particular junkyard trip. My default junkyard toolbox, the one you've seen photographed next to so many Junkyard Finds, is the small S-K ...

For the box itself, you really can't beat the old reliable military ammo can. These boxes are cheap, sturdy, and waterproof. I've got a couple of them I picked up at a surplus store who-knows-how-many ...