What is one essential that you should take with you on every hike? A whistle! 
Whistles are small, lightweight, and can be a lifesaver in an emergency.
I used to have an old slightly rusted aluminum whistle that only made a little bit of noise.
Now, I’ve got a Fox 40 Sharx whistle that just about killed my eardrums when I tested it. However, that is a sign of a very effective whistle.
Check out my full review of the Fox 40 Sharx and find out why I have one with me every time I hike, plus another one on my keychain that I take everywhere with me!