Sleeping bag on bottom, everything else on top of that.
I was an RTO in Ranger Batt, so I always had a top heavy ruck.
I was always taught to place heavier items on top, and to always use the waistbelt, as to place the weight on your hips.
At Lrs we would always take the flat bottomed "assault pack" from the CFP-90 and rig it on top of our Alice pack as to carry more gear.
A quick deployable woobie fit nicely in the outside pocket of the assault pack.
