With all due respect, I'll disagree - water is certainly important, but in my view it is not the first priority.

This is all assuming that you've found yourself in a survival situation and have stopped and admitted it to yourself.

The first priority is to attend to serious health issues - both physical and mental. If one of those pressing issues is dehydration, then water indeed becomes an immediate priority. If you've got a PLB along, this is the time to activate it. If the weather is severe, then shelter/body core temperature becomes a first priority.

The second priority is to maintain core body temperature by seaking shelter and warmth (through protection from rain/dew/snow, additional insulation, fire, body-to-body contact).

Of course a fire not only provides warmth, it also helps from a signaling perspective AND it tends to contribute to mental health. Make sure you've safely collected enough wood to maintain your fire over time - so you don't have to try to find wood in the dark. Make sure your fire is under control - especially in dry conditions.

The third priority is signaling and making yourself visible for rescue. This assumes that if you can get rescued soon enough then water will not be an issue - pending priority #1. Part of this depends on the trip plan you gave a responsible friend ... if you won't be missed for several days, then you may be forced to hold off on signalling until it is more likely that someone is looking for you.

The fourth priority is water, though if your means of collecting water is transpiration bags, then you would be best to put those in place after shelter/warmth is available so they have time to do their thing. It is important to keep safety in mind when collecting water - making sure not to fall into dangerous waters, not to get wet and risk exposure, and not to get hopelessly stuck in muddy banks or wetlands.

A fifth priority might be food, if conditions warrant its collection.

At least that's my view of it. If you haven't read Cody Lundin's book, I'd recommend it.