I've used the apple sauce packet for fuel alcohol storage. In fact I have a partially full one sitting in my gear room to test for leaks. Yes, it would be nice to see how much is left, but, if you premeasure you're fuel before the trip and measure at each burn you should be ok.
Regarding the Rum Runner, I purchased some 8oz flasks a few years ago and have used them successfully with drinkable alcohol, but for denatured alcohol (Sunnyside brand) the plastic will slowly decay. After my first trip with using one as a fuel storage flask, the plastic was becoming milky. It could have been my brand of fuel which cased the problems, but I would not risk it on a trip.