1. Stop at a gas station and approach someone who is filling their car. Ask them to add gas to your fuel bottle (bring a small funnel) and offer to pay for the 1 qt or what ever it takes. The cost should be less than $1 even at today's prices.
2. Stop at a gas station and go around to all of the pumps not in use. Remove the nozzle from the pump and drain the residual gas into your fuel bottle. Many people replace the nozzle without draining it and a few pumps may provide all you need free.
3.In any commercial or public campground, find someone with a Coleman stove or lantern and offer to buy a small amount of Coleman fuel from their large can.
BTW, denatured alcohol (ethanol treated to be non-drinkable) is available in most hardware and home center stores in the paint section, often in 1-qt or 1-pint cans. It is the solvent used for shellac.