It's almost certainly an army blanket, probably safety pinned at the neck to hold it in place. They are fairly typical Mujahideen gear, since it is cold up in those mountains. But traditional craft Afghan blankets are usually more colourful than that, so it's not a typical 'tourist purchase' Afghan blanket, more likely an old army surplus one, possibly something the Russians left behind in 81 when they cleared out, or maybe taken off a dead soldier from the Soviet-Afghan war. If you do a search for a 'Bulgarian Officer's blanket' you'll find those are the same colour as the one in your picture, in fact they are darker on one side than on the other (to suit different terrains), but it'd be a good lookalike, and very warm too, since they are wool (heavy because of that as well, i.e. quite a few lbs in weight).
You may find this link useful too (there are several pages of pics of Mujahideen soldiers, but be warned before you click on the link, one or two of the pictures are of a fairly unpleasant nature, i.e hangings and such - they are war images after all, so if you are squeamish, be ready to close the window):
http://flickrhivemind.net/flickr_hvmnd.cgi?method=GET&page=1&photo_number=50&tag_mode=all&search_type=Tags&originput=mujahideen&sorting=Interestingness&photo_type=250&noform=t&search_domain=Tags&sort=Interestingness&textinput=mujahideen
