Yeah, truly the water filter is the most important thing to protect. I usually have it in a baggie, in my pocket. However, it's not unusual for it to drop to the 20's or below overnight, even in summer. I probably shouldn't worry about the bladder except if it's close to depleted.

I'll still stuff extra clothes, stuff sacks, etc. in the pillow, but I've shifted to wearing more to sleep and bringing less extra clothing, so I'm looking to use the bulk and weight.

I'm glad I'm not the only one who's thought of this. Even so, I'll just try to be careful and try it on a warmer, low-risk night.