I have the ACT Light SL version - with a slightly slimmer back for ladies! It is plenty big enough for 2-3 day/nights out with room to spare. The pack is very stable on your back which is good for scrambling and has loops and hooks for both walking poles and ice axes. There is a handy pocket on the waist strap which is good for your compass (or jelly baby's!!!)
The only extra thing I might want on a sac is a map pocket (but thats just me being fussy!)
(Written by: bryetta)