I'm forced to agree with Pleater here. Leather is just about the hardest wearing material you're be likely to find, even today, but ESPECIALLY by the standards of 17th and 18th centuries. It also has the added bonus of being relatively easy to make, craft, and is a by-product of sheep or beef (so all those cattle rustlers would have the opportunity )

If you were making your bag by hand, and didn't want to have to RE-make the bloody thing in six months time, you'd pick the hardest wearing thing you could find. All the better if you didn't need to BUY any material to make it with.

Of course, there MIGHT have been bags made out of other materials, but most of those would have rotted away centuries ago, so we'll never know about it.