Andrew,

I wear such a vest when flying, except it's for my survival equipment.
It's not terribly convenient for use to reach stuff I need when flying,
other than a pen or pencil. (For cockpit organization, I've observed
that the vast majority of pilots simply carry too much crap - by
getting rid of half of it the whole question would be less of a
concern.) Because the guys who have done research into post crash
survival have indicated that a large percentage of the time you only
have acess to what you have on your person - you can't get at the
survival pack or it gets burned up in the crash - I've taken to putting
the basic equipment into a vest that I put on just before I get into
the airplane and take off after I get out.

There's some absolutely excellent information provided by the nonprofit
organization that does research into survival equipment and practices
for aviators: Equipped to Survive. Take a look at its website:
www.equipped.org

All the best,
Rick