Sleeping bags and sleeping systems can be quite sophisticated. Which of the following accessories or add-ons are important? How important is simplicity in this context, eschewing most if not all of the options listed below?
What about the following zipper options?
What about the following design elements at the top and bottom of the bag?
What about the outer shell?
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.