As you're finishing up the winding of the rope to bundle the coil, and you have two short strands left for wrapping around your body to wear it: Make a bight with the two strands, put it through the top of the coil in between the middle where its bundled and the top of the whole coil. Put the strands around the opposite side of the coil so that they go through the bight, pull all that through the bight. You should be able to hold the strands and let that whole assembly hang in the air. Then over your shoulders and around your waste with the excess. Can't visualize what I describe? Youtube the rope back pack.
Coiling from the middle is nice for a quick rope backpack. When it's time to flake the rope and climb later the pack blows. It takes longer to make a pack if you start from one end coiling with a single strand but then when you use it later it won't come out in a tangle.
whats a better finishing knot to use? Every single time I do this after about 10 min the knot has slipped and the rope starts the inevitable journey down the back of my legs. not a big deal if its 10 min the crag but if its miles in and out then it starts to really suck.