I use Stabil in all my "utility" gas cans. I used to just put it in before winter, but still had some un-stabil gas in some small engines and got gummed up. I now put stabil in ALL my gas cans for use in my tractor and all small engines. No gumup problems since.
There might be something better, but Stabil works fine for me.
Ben
the stuff is sort of messy/stinky and tends to blow out the top of the little dispenser thingy in hot weather though.