IT Clips uses two small plastic clips to turn a used tube into a strap.  Simple enough, and their site lists tons or ways to use it: like straps for your bike rack, a belt, pant leg strap, sleeping bag strap, etc.  They’re easily adjustable for length, and you can hook more than one together to make really long straps. From the looks of ’em, they’re made for road tubes.
They’re sold in sets of two for $3.99 and come with two little hooks, so you can turn old tubes into bungie cords.
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