My backpack is an Equinox Katahdin ultralight that weighs 26 ounces. I turn it inside out, put my sleeping pad inside and roll it up. I cover it with a plastic bag and strap it to the top of my rack. My gear goes in my panniers. I've only used this for a three day excursion where I had a safe place to store my bicycle gear. Which brings up the bigger issue - safely storing your bike while backpacking.