Hi Trish -
If you're not a natural seamstress, as a possible alternative, take a look at this extremely lightweight, strong and scrunchable-to-a-very-small size bag that I used all the time on my recent 'working not walking' Camino when I volunteered at one of the albergues in Rabanal. I was frequently asked where I'd bought the bag.
AUD$12.95
The Bubble Bag is an amazingly innovative bag that expands as objects are placed inside!
Made from sturdy polyester the Bubble Bags have a long shoulder strap and are ideal for shopping, gym, or the beach!
Available in 6 colours, simply scrunch up the bubble bag when it's not in use for easy storage and keep one in your car or handbag so you will never be without!
I used mine every day. If I nipped around to the shop to get the fixings for lunch - jamon, cheese, lettuce, tomatoes - into the bag they went. Ditto for the tinto! Into the bag it went! When on my dinner break I'd take the ipad and my wallet etc in the bag. I would often tie the long shoulder straps in a knot and then sling it over my shoulder, or tie up as you would do with a gift, and use it as a clutch bag. I checked the weight of the bag on my kitchen scale and it's 35 grams. The bag is available from annabeltrends.com but you might also be able to pick one up at a homewares shop near you in Melbourne. The uses are endless. I've had mine for about 5 years now and it's always in my handbag.
This is my bag, empty and laid flat. The dimensions are 22cms x 17.5cms, and as you will notice, mine has stretched a bit over the years - probably a few too many bottles of tinto in it over time!
I hope that this helps if you decide not to make a silk bag yourself. Best wishes with it if you do - it will be a lovely and unique bag.
Cheers - Jenny