grr. srry to keep posting thoughts in seperate posts but I will also mention that the leatherman/gerber pouch also makes a great handgun mag pouch for when you have a hard time concealing your extra mag.
I carry this in my truck all of the time. It is big enough to carry a few mags, IFAK, Survival gear, and a few other items and still not be too big. It is a good bag and does not look too MIL.
Seen Here:
http://www.skdtac.com/ProductDetails.asp?ProductCode=EAG.565
I would look into something that can be easily thrown over a shoulder that could carry 2 to 3 mags, a first aid kit, and a small survival kit. There are a few readily available solutions from go-bags to bandoleers.