I've done some overnights with small climbing packs. I kept to the ultralight side of the trail and was fine. I've done the same a fer times on my bike in lieu of panniers (which I don't have). You might want to look at the Patagonia Ascensionist. Strap a pad or small tent outside and your good to go. Under 17-18 lbs. is usually not too bad on the shoulders.