I pack depending on the weather, and how much I feel like carrying.

Bags (one of these):
Western Mountaineering Iroquois (38 degrees, down)- I probably use this 70% of the time.
Western Mountaineering Antelope Super Microfiber (5 degrees, down) - My winter bag.
Sierra Designs Wild Bill (20 degrees, synthetic) Only carried if it's going to rain all week, like in the Smokies in springtime.
Eastern Mountain Sports Alpine (40 degrees, synthetic) Same as above, and also used for canoe trips.

Pads (one of these):
Thermarest Pro 4, full length self-inflating pad
Ridgerest Deluxe, full-length foam
Ridgerest shorty, 3/4 length foam

Bivy:
I'll carry an Equinox bivy if I'm sleeping under a tarp or might use a trail shelter along the AT. It obviates the need for a groundcloth, and the breathable fabric does a nice job of adding warmth and keeping off any rain spay if it's really coming down.