Ditty bags are easy to find at most outdoors stores. We picked up a pack of three smaller ones at Big5 for under $20...one we use for a NeoAir, one for my wife's down jacket.

The third one sits on the desk in our library, waiting for someone to find a use for it
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Check our our website: http://www.backpackthesierra.com/

Or just read a good mystery novel set in the Sierra; https://www.amazon.com/Danger-Falling-Rocks-Paul-Wagner/dp/0984884963