Pilots are my inspiration mainly for the first layer by the way. I've read countless reports on downed pilots who had their gear off their bodies. Guess what? They didn't have their gear on the ground. It was destroyed or missing.
Keep your essentials on your body. If you survive the crash, you'll have your most important items with you.
Also, depending on what happens, I may have to drop my pack, and I cannot walk around with it on my back all the time either.
I do plan to add a "middle" layer though with a combat belt setup. They are called "battle belts" apparently, but I haven't decided on what all I'll put on it.