Hi Kevin,
While we don't have a backpack-specific guide, the material you described looks like it matches the Patagonia jackets we made guides for. Check out the Tenacious Tape we used in this [guide|19437|jacket patching guide], and see if that's a good solution for you. You can also get [http://www.amazon.com/Singer-5-inch-5-inch-Iron-On-Patches/dp/B000RF0RG0/ref=pd_sim_ac_1?ie=UTF8&refRID=0TKGM5Q57A0XRXXNPCAK|iron-on fabric patches] to better match your backpack, but if the original fabric is thin and the patch is thick, you risk tearing around the edge of the patch.
Hope that helps!