I don't know if this is the right way, but I'd roll the egdes up together and use a blanket stitch to bind the roll tight ... then very possibly watch the whole thing fall apart as soon as I put anything in ... but that's where I'd start. It'll be something simple and efficient, I expect, given how sacks are/were made and in what numbers.
Hang on ... There are some coffee sacks downstairs my daughter brought back from somewhere the other day (coffee shop, I am guessing, who knows) and I am sure I still have some old French mail bags somewhere. Let me look. Maybe a photo later on.