It goes without saying that being able to light a fire is essential in most parts of the world (an exception being the possibility of extreme changes in the weather as a cause for the apocalyptic events in which case keeping cool might be a greater challenge than keeping warm).

Lighters and matches are good for the beginning but they won't be around forever. You will have to learn how to light a fire without them eventually. Wherever possible, try to learn this before escaping to the wilderness.