I think zippos are a neat and durable design, but absolutely horrible for survival use. Even if it's fully filled with fluid, it will evaporate in a matter of days whether you use it or not. For the same space and weight you can fit lighters, matches, and tinder, all of which have a shelf life of years and can be rationed as much as you need to. Carrying spare fluid is bulky and heavy compared to the alternatives, and there is always the chance of it spilling. There are many good options for survival firestarting(I prefer a bic or butane lighter as primary, with a firesteel, tinder, and storm matches as backup), but I would put Zippos at the very bottom of the list. I would sooner pack my bow-drill set.