What about the following zipper options?
· snag free zipper,
· left and right hand zippers for zipping two bags together,
· two-way zippers for ventilation,
· draft tubes to cover the zipper,
· quarter or half length zippers to save weight,
· ¾ or full length zipper in order to use the bag as a quilt?
What about the following design elements at the top and bottom of the bag?
· hoods (yes bags are available without them),
· a hood that folds flat on warm nights,
· draft collars,
· chest pocket for small items,
· extra length to store extra clothes or boots,
· draw strings or zippers in the foot box area for adding or subtracting foot room and for increased ventilation?
What about the outer shell?
· dark colored shell to absorb radiant heat from the sun,
· waterproof and breathable shell covering for sleeping out in the open,
· waterproof and breathable shell only at the foot and hood with a water resistant body,
· built in pockets for a sleeping mat and/or a pillow?
The above options only cover a part of the accessories commonly available, but you get the idea. Click on this link for an overview of sleeping bag/sleeping system designs: Alternative Sleeping Systems.