The debate so far has focused on woolen blankets, bedrolls and heavy winter coats - I don't think that has a whole lot to do with ultralight backpacking. Apples to oranges...
A horseshoe (Rrussian "skatka") backpack would allow to reduce the backpack's dead weight practically to a zero, as a sleeping bag and/or a tarp or/and a tent can be easily rigged into a good backpack. That will definitely require some new skills polishing, and not only in the packing art, but also in an efficient carrying and using such a thing as well.
YMMV, but you're not really going to rig a sleeping bag or tent into a *good* backpack. A bedroll slung over the shoulder horseshoe-style is a convenient, compact method for carrying stuff like tarps, blankets or clothing. Note that this was the way soldiers carried (rain)coats, blankets, shelter halves, etc., even when they were issued a backpack (knapsack/haversack). In that case, the horseshoe roll was attached to the top and sides of the backpack. But do note that the rest of gear was still carried securely inside the backpack.
http://www.forgottenweapons.com/wp-content/uploads/2013/03/1945q-450x277.jpgAs a stand-alone means of load bearing though, there are serious limitations as to what can be carried comfortably inside a makeshift bedroll "pack". Certainly no larger, bulkier items such as pots, larger cooking utensils, water containers, food, etc. Also, a bedroll is not nearly as secure as a proper backpack. Easy to lose small items without noticing. And any time you need to get something from your pack, that will mean taking apart the entire bedroll, then carefully tucking it back together before setting off again.
So where's the point? A small military surplus canvas backpack weighs nothing. Speaking of the Eastern Bloc stuff, the old Soviet veshmeshok is dirt cheap and extremely lightweight.
http://www.ebay.com/itm/Soviet-Russian-A...W-/251763539549 Plenty more comparable (also better) designs out there, too. Now that I think about it, I must be an ultralight hiker myself because I prefer a shoulder bag to a rucksack for easier day trips. A lightweight canvas gas mask bag (Indiana Jones style) suits me just fine and still allows me to keep my gear organized and instantly accessible. As for my sleeping bag, I'd rather carry it stuffed safely inside the waterproof compression bag until needed...
One way or another, it's all a matter of individual preference. But if you want to go absolutely ultralight, the best way would be to dispense with that sleeping bag, bedroll, tent... altogether. It is perfectly possible to make an improvised shelter in most kinds of terrain that will keep you alive through the night. But I don't genuinely think caveman camping is for everyone... Neither is the ultralight cult.
