What you need1 old, full length Parka.
Any bright lining, contrast fabric you want
Matching Sewing thread and machine
1) Lay out your coat flat on floor and take a good look at it, imagining it in peices, not a whole.
2) Cut a large front section with pocket to be the front of the bag. 30cm wide x 40cm long.
3) Cut a long back piece to be the back of the bag, including the part that will fold down over the front. 30cm wide x 60cm long. plus a matching size in the contrast fabric.
4) Cut the sleeves cut to width 20cm, for the side panels, I included the cuff buckle.
5) Cut 68cm length of buttonhole section from down the front of the coat as a handle. Plus a matching length of contrasting fabric
6) Sew the two ends of sleeves together, leaving the cuff end as the top part of bag sides.
7) Attach front panel(with pocket) to what you designate as front of side panels, fold over any spare at top and sew, do this double thick stitching.
8) Attach contrast fabric to back panel (face both back to back, stitch, turn right way round) and do same to buttonhole handle.
9) Stitch back panel to side panel so you have a long flap hanging over the front.
10) Attach handle to side panels, add Velcro to front as easy fastener.
NB: Im imagining most people to this site will be reasonably good at sewing, if new, try this with paper and sellotape first, to get the 3D feel of it before cutting up your coats.
I didn’t measure as I went along, I approximated, if you want it smaller , bigger, whatever, go for it!