How to pack MagSafe cable to prevent its breaking?
One method I use on all my power adaptors is to loop the cable and secure it with a piece of Velcro. I will generally either keep folding the cable in half until it is a bit longer than fist size, or just loop it back and forth in a “S” pattern that is about fist size. I do NOT loop it in a circle.

I find these methods keep the cord safe and tangle free, allow quick deployment, and don’t put pressure where the cable comes out of the adaptor. I have never suffered from frayed cables using this method.  If you don’t have a Velcro strap, a rubber band will work. 

Here's a photo of 2010 adapter that has been deployed around the world. Dirty, but fully functional, and no frays!