Things I found missing from Dark Heresy that I use to make my campaign interesting:
Speed Loader for Stub Revolvers (gear)
Cost:
2 Thrones each
Result:
Reload takes 1 Full Action rather than 2
Uses:
Pre-loads 6 rounds, great for special ammunition; screw locks the rounds into place, unscrews to release.
Spring-Loaded Pistol Harness (upgrade)
Cost:
100 - 150 Thrones (Common to Good Quality - custom job)
Result:
Drawing the attached pistol counts as a Free Action without the Quick Draw Talent
Uses:
A Compact pistol is stored on the underside of the forearm, a la Desperado; with a flick of the wrist, a spring-loaded rail puts the pistol in the user's hand... the pistol MUST be Compact, and cannot be reloaded while in the harness. If the harness is jarred while locked there is a 30% chance it will spring.
Mono-filament Wire (weapon)
Cost:
5 - 20 Thrones (Poor to Good Quality)
Result:
1d5 R damage, Tearing, No Additional Penetration
Uses:
Must be able to put the wire around the intended victim's neck and pull back hard; the wire only affects the neck, so Critical Damage that kills always decapitates with gurgling and lots of blood.
Duct-Tape (gear)
Cost:
1 Throne x 30 yards
Result:
Should be self-explanatory, really, and its up to the creativity of the players to make it good
Uses:
Comes in Matte Gray or Matte Black
Flare Pistol (gear/weapon)
Cost:
20 Thrones, 1 Throne per Cartridge
Result:
30m, 1d5 E, Primitive, 0 Pen, 1 Clip, 1 kg, Average, Solid Projectile
Uses:
Fires a single cartridge into the air, which burns hot enough to be seen up to 5 miles away; when fired at someone, treat as a Photon Flash grenade. If fired at flammable materials, they will burst into flames.
Sure, these things seem a bit odd to find in the 40k setting, but even the most mundane has its place.