OK This "tutorial" is mostly for @
halliwax since he's making a bottle too, but if anyone else is ever interested, here's what I came up with.
3D models of the bottle parts are here
https://www.thingiverse.com/thing:2843583
Bottle is here
https://www.amazon.com/dp/B01MRNUJH2/ref=cm_sw_r_cp_ep_dp_XuPXAbSYBVQWH
The finished [p]leather band should be 41mm wide. To make mine look a little nicer, I doubled that and folded it over on itself to give it some extra thickness and so that it's leather on both sides (when looking through the glass to the other side, you see [p]leather on the inside as well instead of the fabric lining). For the width of the bottles I have, I cut the band at 12 1/2 inches by 3 1/4 inches, then ran some glue long the fabric side and folded it over on itself to make a double sided leather band 12 1/2 inches long by 1 5/8 inches (approx 41mm) wide.
Now, you need to make a triangular point on the left end of the band. To get the correct angle, mark a line 40mm from the end, then come in at angles to the center and cut to form a point.
Next, curve the band around (you can use the bottle to ensure a tight fit) and overlap the pointed end over the other end, and glue down with super glue. Don't glue the strap to the bottle, you want to be able to remove it so you can adjust, wash, etc. Just glue the strap to itself to form a loop.
For the strap, start with a piece of gray 1" nylon webbing that is 28 inches long.
Mark a line at 8 inches from the left end, and another line at around 11 3/8 inches from the left end.
Run the webbing through the band as shown (note the orientation of the pointed end), and line the end up with the 8 inch mark. Secure with some super glue (you can add a rivet later)
Next, fold the right end up and line it up with the 11 3/8 inch mark. Secure with some super glue to hold it tightly in place. You should end up with something like this.
Next, crease the double layer of webbing where the strap ends and tie some waxed hemp twine or leather around it with a double knot. Leave a loose end for later.
Then wrap the twine messily and randomly around the webbing, crisscrossing a bit. I did about 15 wraps. You want to end up with a wrapping that is approximately 21 mm wide.
On the last wrap, I threaded the end of the twine back through the crease (under the wrapping) and back over to duplicate the visual dictionary image. Then I tied that loose end to the original loose end from my first double knot.
And there you go! all finished. Add a rivet (I think it's a rivet) or other fastener to the first loop if you want to be super accurate.