If you need a solution to an industrial-grade fabric need -- like rebuilding a backpack or hanging a heavy rug from the wall -- Seattle Fabrics is the place to shop.
In addition to stocking all kinds of heavy-duty fabrics - Gore-Tex, coated nylon, etc. - they also have a wide range of nylon webbing, buckles, grommets and fasteners.
The staff is extremely knowledgeable, and can help you select the materials appropriate to your project. If you're interested in sewing your own outdoor clothing and gear, they also stock some sewing patterns to choose among.
Let's say you wanted to hang a heavy rug from your wall. Just head to Seattle Fabrics and pick up a length of 2" velcro tape. Hand-sew one side to the top edge of the rug and tack the other to a 1 x 2 strip of wood (both the wood and the short upholstery tacks used to attach the velcro are stocked at any hardware store). You can then nail the wood strip to the wall wherever you want it, and attach the rug using the velcro. This will hang even a heavy rug securely, without damaging it, and allowing you to easily remive it for cleaning, etc.