Step 1: Peel the Bark From your Victim
Use a knife slowly separate the bark from the branch. then Scrape any left over material off the bark with the knife
Step 2: Make the Top and Bottom
Cut 2 1/2 inch discs for the top and bottom of the flask
Cut 1 1 1/2 inch disk for the plug
I used a hatchet to break up the plug piece to larger than the finished size. I whittled the plug down to size using my knife (Be safe here and don't cut your hand). You could start with a dowel here and whittle it down to make it look "Hand Made"
Drill a hole in the top disc to hold the finished plug.
(You could dispense with the top and make a pen cup for your desk, or a drink holder, it would be a posh Starbucks caddy)
Step 3: Soften and Sew up the seam
Use a large needle (Glovers, sail etc) to stitch up the cut side.
I used a natural Hay Bailing twine and striped off a few fibers, softened them in the boiling water, twisted them and went to town sewing.
When Finished, insert the top and bottom (sand/file as necessary or apply some more steam to soften the bark)