Hey Jon M
Well good question on the xmas tree. FIRST look at how you place or configure your Saftey gear. Where is it, can you reach it with eyes closed without hesitation. Most recreational dive BC's, have pockets. So one would assume you place some items in them. Which are hard to get to in a pinch because it is high on the body as opposed to on a leg. BUt in most cases. Alot of stuff is clipped where ever a D ring is. SO infact you are already a tree of sorts.
TO answer you saftey question. this is what I have. First I dive a BP/wing rig. Single tank, So no pockets. I do have pockets on my dry suit and a thigh pocket when I dive wetsuit.
Main gear, One cutting tool on my waiste strap, just left of my buckle, one SMB tucket behind my back in a backplate pocket with a spool reel attached for quick deploy, one Computer on my right wrist and also a bottom timer on the same wrist. One compass on the left wrist. In my left pocket. One spare mask and one finger spool. In my right pocket one slate and one Z knife tied to a bunggie and is easily deployed. I have two back up lights one on each harness which is tucked neatly under each arm. low profile and easily deployed. Plus a can light on my right side neatly tucked.
As this goes I am not a xmas tree and I have redundant gear for that Saftey factor. Plus I have a buddy as another redundancy. I have nothing dangling.
So to sum it up. One spare mask, one SMB, two backup lights one compass, one back up timer, one back up cutting tool. And a whistle in the right thigh pocket attached to a bunggie. Depending on the dive I carry the appropriate gear and it is all neatly stowed away.
Safe dives