I also like a bag liner. I use a Cool Max Travel Sheet and carry it along with some other insulation. If it's warm enough, I just use the bag liner. Then I also have a military poncho liner that I'll use, too, if it's a little chillier. If I'm prepared for cooler temps, I'll bring my summer weight bag, and if I think it'll get downright cold, I'll bring the heavier-duty bag. All my stuff is synthetic, so it doesn't pack as small as I'd like, but I'm cheap, and I also tend to avoid camping in too cold of weather, so it's not that bulky. I think carrying multiple pieces of bedding bulks up your gear as well, but it's also more versatile. I went for a long weekend a few weeks ago and took the summer-weight bag, the bag liner, and the poncho liner. Temps dropped lower every night, and I think I started out the weekend in the bag liner and ended the weekend sleeping under every piece of bedding I had. But I was comfortable every night, so it was worth it. If I had only packed for the coldest night, I would have had only my heavy-duty bag and bag liner, which would have left me choosing between too warm and too cold on the warmer nights. Also a light, wool base layer might not pack too large and might be useful if temps drop lower than what your bedding is good for.