I discovered this bandoleer system at a gun writers gathering I attended a few weeks back. I brought one home with me to check out and it has quickly become my favorite method for carrying spare magazines when I'm out and about with a rifle.
They make them specifically for your type of rifle. They offer pouches for the AR15, AK47 and AK74.
It's so simple and useful it makes me think, "why didn't I think of this?"