I found that my Barley was adequate for the BCM last year. I did leave behind some stuff that I was planning to take, namely spare socks, shorts and shirt. If it rains, this stuff would be really handy. Otherwise, I can wear the same pair of shorts for a week and not be bothered (others might be by the smell
).
Smaller headtorches can save you a fair bit of space.
Do you really need spare batteries?
This stuff saves a very small amount of space. 3 AAA batteries take up next to no room compared to a jacket or a pair of shorts. My advice is that you take enough clothes to survive down to about -10 and wear most of them all the way round, hence saving space in your bag.
I take about the same amount of kit on a 200 as on a 600. Some people take very little stuff, I almost got crucified on ACF for suggesting that a Barley is a good idea for audax.