And then I made dozens of bags - some large, some small - and all with elasticated tops. I used my overlocker to do the side seams, and finish the top edge. Then I folded over a casing and stitched on my regular machine. Then I spent a couple of evenings threading the elastic through.
In the end I only used up about 12 metres - but I am glad that I have found a useful purpose for it. You will have to wait till after the weekend to find out what that is.