If you were looking for a single skill in general then i would suggest Wild Food, finding plants that you can safely eat in the wild is definitely the best option i know its not quite as exciting as tickling a fish but it will serve you a lot better in the wild.
Fish tickling is not great when your outdoors in general in my opinion. You end up spending a lot of time with your hand in the water, which may not be a problem in high summer but doing so in winter for most of the world will be a bad plan if not dangerous, and you need to be 100% about that fish and not doing other things
Learning to make line and hooks on the other hand means you can set up a net/trap/line, and then go about your day improving your shelter or boiling water etc. then come back later and see if you caught a fish