What are some survival myths that are completely wrong and could be life-threatening?

• Don't try to escape from a deserted island. You'll almost certainly die before anyone finds you.
• In Australia, there's no need to try to identify or catch the snake that bit you. The antitoxin is the same worldwide.
• "Punching the biggest guy on your first day in prison" is not a good idea for survival there.
• If you're driving during a tornado warning, don't get out of your car and go to the side of an overpass to "hide under it." This myth became famous from an amateur video of a man and his daughter hiding under an overpass, but the overpass they chose had an unusual structure that saved them. Wind speed increases as you get closer to the ground, and the narrow passage creates a wind tunnel effect, which can also send debris picked up by the tornado flying straight up at speeds of over 200 miles per hour.
• If you were ever stranded on a deserted island, building a raft and sailing to civilization is not a wise strategy. You would likely never be found, or you would become extremely dehydrated and almost certainly die. You should stay on the island and be found alive.
• If you get lost or your car breaks down, walk to a safe place. Stay in your car. Your car will always be found, but you alone may not be. Unless there is an imminent danger such as a wildfire or flood, stay put. Walking around consumes a lot of energy and increases the risk of injury or getting lost again. Your car is a safe haven and is much easier for rescuers to find.
• Do not drink "cactus water." It is not potable and may cause vomiting, diarrhea, and further dehydration.
• If you are truly suffering from diarrhea, simply drinking water is not enough; you are also losing large amounts of salt and electrolytes, and failing to replenish them can lead to serious problems.
• "To find water, follow the birds in flight." They're everywhere.

What are some little known survival tactics by prey animals?

 Some ducks practice what is called unisphereic sleep.

When they form a line to sleep, the ducks at the end will often have one eye looking to the outside. The half of the brain that controls that eye will stay awake while the other half goes to sleep.

It’s a tactical formation: a line of ducks sleeping, while a duck on the outer end is keeping a lookout for predators while the remaining ducks sleep normally.

It’s remarkable because - ducks aren’t particularly smart creatures - this behavior has been ingrained and then reinforced through reproduction. (Half-Brained Ducks in a Row. Science Magazine. Mackenzie, Dana)

Sleeping with one eye open - is literally a thing - created by evolution.

But I’ll raise the stakes. Here’s something even better.

Some birds, that engage in super-long flights that last for weeks, even months engage in unisphereic sleep.

Scientists strapped a EEG detector to a frigate bird − those birds with strange, inflatable necks.

These birds are capable of flying for weeks on end. The EEG detector monitored their in-flight sleep patterns:

Noting that it would put one side of the brain to sleep as it navigated (just as dolphins do, to go up to breathe while sleeping), avoiding collisions with objects and other birds.

Some birds even have the ability to go completely to sleep, both brains asleep, while still retaining their GPS capabilities. (Evidence that birds sleep in mid-flight.Nature Communications volume 7. Neils Rattenborg.)