If you have an older NON "dual fuel" Coleman you don't want to use pump gas in it. Not only will it eventually foul the generator, but I recall the manual saying that the gasoline carb/FI injector cleaners will eat up the lining on the interior of the fuel tank, subjecting it to corrosion (when empty, at least).
Never buy the little plastic bottle of Coleman fuel. Long term, it's not fully impermeable to naptha! Leave it sealed in your garage for a few years and you'll pick it up to find an intact foil seal on the bottle top but NOTHING in the bottle! Ask me how I know....
Still can't beat the old metal can.
I use Coleman fuel for both my lantern and stove. Can't beat the stuff. I HATE 1# LP tanks, but am stuck with them for my portable water heater (popup camper with no onboard HW).