I have a Lafuma 40 degree bag that I bought from the REI outlet; it weighs just over a pound, and keeps me warm in nice weather. Plus, it packs down to the size of a nalgene. Of course, my other bag is a rather heavy winter bag, so I do my very best to use the summer bag. This has led to more than a few colder nights than I would like, but I've had reasonably comfortable nights down to below 30, I just had to be fully clothed and wearing my jacket, beanie and gloves