I had very little gas after the Naches run in October. I would say that it would be a slim chance of running out of gas on most trips. However it is not far fetched to come dangerously close to running out in the backcountry in central or eastern Washington or Canada. Make a wrong turn on a forest service road and go 20 miles out of your way and it may turn into a long hike. It would be unlikely for me to carry 10 gallons of gas on a noraml PNWX planed wheeling trip. However, if my wife and I are out exploring by ourselves, the extra gasoline might be great for peace of mind.
Thanks for everyones inputs!
Bryan