I have used a "messenger" style bag while working in the field for years (almost always with a day pack as well). I am a geologist and it carries my field tools, sheet holder with maps and paper as well as my field book. Pete has enumerated the advantages well. Using a pack for such work is very much a hassle. It does not carry well in front if you are using it a lot. Carrying your "stuff" all on belt, slung separately, etc. is worse. It is also convinent to take it all off when you stop or are using a vehicle for transport from one area to another. I don't know anything about Cody or his use, but I find that there are some uses where that style of bag is superior.

Respectfully,

Jerry