I belong to the school of thought that doesn't bring anything not part of the dive plan - and safety equipment is definitely part of the dive plan even though I very much hope not to use it. I probably still take things I don't need, but I try not to.
On a typical Lake Erie wreck dive I carry:
Line cutter (on right shoulder strap), dir knife (left waistbelt), whistle (left shoulder D-ring), backup doublender (right shoulder D-ring), light (primay or backup depending on conditions, mounted right D-ring), glotube (better than a dive light for seeing your own DC/spg, mounted left shoulder D-ring to be closer to DC/spg);
Wrist Slate (left forearm), DC (left wrist), watch (right wrist), Compass (right forearm);
Example specific add-ons:
DSMB w/ spool (right wetsuit pocket)
Pony Bottle (slung left side)
Further accessories would only be added if part of the dive plan (including safety contingencies). Reels, spools, camera, additional slates, signal mirror, buddy line, EMT shears, PLB, lift bag, second DSMB, etc.