In reply to niallk:
Unless it's cragging with an easy decent or abseil, I'm reluctant to leave my sack, in case I can't easily retrieve it.
Like others I have learned from mishaps in the past, trying to get back to my sack have involved long and knackering detours when all I wanted to do was get back to the car!
Most decently packed climbing sacks will be almost empty by the time you gear up.
Once the hip belt and lid are folded away and the sack is compressed, you will hardly notice it.
On Scottish, Alpine routes with ab stations I use a BD Bullet 16 litre bag to keep my spare gloves, belay jacket, 1st Aid Kit, headtorch, phone, food and water in.
The bag is tough and packs small and weighs very little. I also save weight in my approach sack by leaving the main sack lid behind and using the Bullet for carrying bit and bobs on the walk in.
Whatever you do, make sure you have your head torch, phone and fist aid kit as well as spare gloves and a belay jacket with you!!!