James,
There are many good gravel bars on the Canning. They change with every season as well, though there are some well used strips there. Well used means well hunted, as well. The last poster has a good point: find out what the land ownership patterns are, and stay on the Arctic National Wildlife Refuge lands. That obviates the necessity for permits. Contact the refuge headquarters in Fairbanks for land ownership maps.
I would be careful cacheing gas in plastic cans out there. As Nizina said, there are LOTS of brown bears in that country, and brown bears LOVE plastic cans. If you cache plastic cans out there, DO NOT place yourself in a position where you HAVE to have the gas contained therein....you may be dissapointed. Metal cans would be my choice for caching in bear country. Alternatively, put a small electric fence around your gas cache.
As Nizina said, closest fuel may be Circle City, and you DEFINITELY want to check on availability BEFORE you get there. One of the 135 operators in Fort Yukon may also sell you some gas, but they're in and out at that time of year. They're also the best source of information on landing sites. Kirk Sweetsir is the expert on that part of the world--give him a call, he's a great guy and very helpful:
http://www.yukonair.com/. I don't know if Kirk will sell you gas or not. He has bulk tanks in FYU.
MTV
MTV