In reply to Anhibian:
For winter, from bottom up:
Silver survival bag (unless we're cutting grams)
Lightest cheapest throwaway waterproof trousers
Spare gloves
Goggles
Belay jacket
Crampons
Winter Rack (set of wires, torque nuts, couple of hexes to fill in the gaps, QDs, Bug, HMS, screws, slings)
Half rope either 30m (solo days, mountaineering/moving together, mmmmm... nice and light...) or 50m (climbing)
Proshell waterproof
Water bladder/bottle
Gloves
Hat
2 x torch
Compass
Lunch
Axes, helmet and gaiters strapped outside, map or guidebook in softshell pocket.
All this in a 35 litre pack (just). Have I forgotten anything? It would all go much better in a 40 litre. Sometimes it's easier to just wear the rack from the off. It seems to me to weigh less on the hips than on the back and creates plenty of space in the pack. Anyone else feel that way?