The sad thing is this is going to turn into another Geraldo Rivera / Capone Vault fiasco. The answer will likely be so mundane compared to the stellar efforts here.
A few receipts, a user manual of some sort, a speed loader, a key that goes to something long forgotten, a few guitar picks, an old zippo lighter, and an old gift card that you forgot to use.
I'm going to say it's spare parts to guns you have upgraded/customized. Mostly 1911 (old triggers, inner parts, barrel bushings) and maybe some from various other guns that you have redone.