Chem Lights
A tool used from everything from Special Operations Warfare to safety at halloween to Rave funness is Chem Lights. They are a great tool to put in your 72 Hour Bag because they are light weight, have no batteries or expiration date and provide a good amount of light for map reading, signaling or using them to allow you to accomplish tasks at night.
Some may know of them by their brand name Cyalume. But push come to shove they are chemical lights. The plastic outer core contains one chemical called biphenyl oxalate. With a suitable color dye and contained within that plastic container is a glass ampule with another simple chemical hydrogen peroxide. When you bend the stick it breaks the glass ampule and the chemicals mix when shaken. The chemical reaction causes light. These two chemicals can be altered with dye to create different colors and even into the infrared spectrum. When the infrared chem lights are used they require Night Vision devices with infrared capabilities to see them. On some missions the military use this technology to mark doorways they enter; dropping an activated chem light at a doorway before a team enters tells other personnel that friendlies are inside that structure. These types of chem lights can also be used to mark a landing zone for helicopters where in the past you would have to ignite flares or pop smoke for a pilot to see. Today military helicopters have the equipment to see these infrared chem lights, keeping the troops safe from being detected by the enemy.
There is a product made by Cyalume which has a handle and strong string attached to a high output chem light. When the chem light is cracked and activated it can be swung around to signal for help. These will last for several hours once activated but once they’re activated there’s no turning it off. So it’s one and done. If I were a boat owner I would invest in these pre made SOS chem lights. When you’re cold and taking on water you don’t want to be fumbling with the fine motor skills of tying a little piece of string onto a chem light in high seas.
If you don’t want to spend the extra money to buy the fancy SOS Cyalume signaling chem lights it’s easy to fashion one from some paracord, light sticks usually have a tab at one end with a hole which when attached can be used to swing them around in a circle, tie them to an object or hang them around your neck. If you have a bunch of the civilian chem lights they also make a great lightweight tool for marking a landing zone at night.
I always try to put chem lights in places where it’s absolutely necessary I have light in an emergency. One place is attaching it to my safe. If the power goes out I can crack the light stick and still open my safe. 
There are also security chem lights. Cyalume makes a special product when used looks like dirt, but as you walk across it the pressure from your footstep activates the chemical and you leave infrared footprints behind. 
There are a bunch of brands on the market, some manufacture their own chem lights while others will rebrand the actual Cyalume light stick. No matter which you buy, make sure it is manufactured in the USA, there is a marked difference in performance between the USA made and ones made overseas. It’s worth the extra little bit to buy the American made chem lights.
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