Water.

Whistle. This is a big deal especially if your hunting in an area with no or poor cell service. Mines on a lanyard around my neck. SOS in morse code is 3 dits(short) 3 dahs (long) 3 dits (short).

Considering that no one knows Morse code, wouldn't long sustained blows be more effective?

Well I don't know. Everyone who reads the post now knows it including you, but I bet more people know it than you think and even if they don't I'm still betting that a rhythmic, continuous signal will draw more attention than just a blasting whistle. If I'm up a tree and here some fool blowing a whistle I'm probably just going to be mad but if I here a pattern that repeats over and over again I think I'd be more likely to wonder what the heck is going on and maybe get down and go investigate.

Anybody who's ever been in the military should probably recognize SOS and I'm pretty certain if GW or any other law enforcement is within hearing he'll come running.

Whether you use morse code or just blast away you should never enter the woods without a whistle imo.

Also, always let someone know where you think you're going to be (of course this could change when you get there and make sure they know that) and when you think you'll be back.

Totally agree. I just would guess people fluent in Morse code is way less than 1% (just a guess). Might as well have a bull horn and speak Mandarin Chinese. I think help will just be coming to noise.

Maybe I underestimate Morse code prevalence

Didn't mean to give you the wrong idea. In no way am I fluent in morse code. I would think that many if not most people know a few words in several foreign languages: gracias, merci, danka, for example. I know one word in morse code and couldn't communicate beyond that word to save one soul.