Littering is illegal and harmful to the environment; that being said, some items often seen as litter can be used as tools in an emergency.
A few items that you may come across when on trails are glass bottles, aluminum cans, plastic water bottles and plastic bags. All of these items are trash that just may save your life.
The glass bottle has two possible purposes. The first is a water carrying device. It’s important not to try and boil water in it though; doing so could break the bottle, causing possible injury and dumping water all over your fire. A bottle can also be used as a cutting device. The edge of a broken bottle is very sharp and can be used to cut cordage and other materials.
Aluminum cans have the same uses as bottles: they can carry water and be used to cut materials. Cans have a few bonus features as well: an aluminum can can be used to boil water in. When polished with a shirt it can also act as a signaling mirror.
Plastic bags have a few uses. Of course you can use it in the way it was designed and carry stuff in it. You can also use it to keep clothing dry in a storm or tie it to a stick and use it as a flag for signaling rescue crews.
The next time you go on a trip, pick up trash you come across on your journey. Not only does it clean up the environment and make it better for everyone else but it can also give you the tools you need in a survival situation.