In reply to baileyswalk:
I was given a 25 litre one of these:
http://www.alpkit.com/gourdon for christmas which I will stuff my das, munchies, gloves, headtorch and drink into. (I really want to leave more behind but don't know what.) It's a bit bigger than I expected (I wanted the 20l, but they are out of stock and heavier,) but packs down plenty small. There are a few other models of small light bags by OMM and Osprey that would work too.
A camelbak without the bladder doesn't fit a Das, (I just tried,) but a rab generator fits fine.
I'm getting a Rab Xenon as another christmas present too, which will be tiny and fit nicely on my harness. (probably in a stuff sack as I like to stick chocolate or biscuits in there too.)