Originally Posted by
tessellahedron
I've stress tested key rings to failure before. They began to elongate sooner than I expected but it took tremendous force to actually pull them open to failure. You can see it happening, and we're taking about forces many times greater than even the tensile strength of the handles on a plastic bag.
The last point is a good one. I'll be stunned if you can do more than a few trips before one of the bags burst when you go over a bump. If you're already overloaded you're not going to get any cushioning from the tires and those bags aren't really designed to deal with sudden forces.
I actually think your best bet is just to get a trolley and walk. If it's only a mile then it's only going to take you an extra 10 minutes and you don't need to be as worried about how to load up and ride in a vaguely safe way.