Even if you’re not an avid cyclist chances are you have one or more dead innertubes lying around. I’ve used one to create a bunch of stretch ties that have held up pretty well. They’re not elegant but seem to work! Bodge or hack, I guess it’s up to you to decide
Using a paper punch I added holes at regular spacing to accommodate different attachment points.
As for the attachment points themselves, I used zip ties clamped around the rails of my bike rack. The idea is to use the head of the zip tie as an anchor point.
Wrapping the strap around the zip tie locks it into place
Ditto for the other end. In no case has this come undone, even in the punishing environment of a bikepacking trip on single-track and gravel roads.
Pretty simple, really. And two seasons of bikepacking have proven (to me, at least) they are robust and trustworthy. The nice thing is if one ever breaks it’s easy to craft a new one, even out in the field.