You'll never have time to grab anything unless you're wearing it, so the vest is the way to go.
LED flashlight that is waterproof, lots to choose from, last forever.
Knife must be instantly accessible and in the same spot always - ie: on your flightsuit or belt - I like the spyderco folding half serrated with blunt nose to cut seat belts - their belt clip is the best I have seen, tight, easy to replace and doesn't come loose.
Sky Blazer twin star flare 4" long, hand launch - a couple
I keep the flare, matches, candle, some first aid, survival blanket in a Coghlan brand 4 1/2 x 5" waterproof pouch, 1 1/4" thick, that fits in a pocket (or vest), which I keep with me ALL the time so I will always have it wherever I end up. It's cheap insurance.
You didn't mention it, but the life vest cannot be self-inflating - most heli ones are not - if they are and inflate prior to exiting, you're stuck.
If you wear a helmet, get an extension to the cord as the 90 degree pull on the helmet cord at the plug in point, when you are getting out underwater will keep your helmet & head & body from exiting. The short extension will keep the helmet cord and extension in a straight line and will unplug easily.
Best insurance is HUET training, underwater egress - got to take that over some of the other equipment - if you can't get out, you can't use the goodies.
Good luck