Yor Friend the Garbage Bag

A wind sock for monitoring the wind direction. Tie the open ends to a pole/stick and place it in the ground.

Not sure what use this would have in survival, but you never know.

CX.

Place the bag inside your backpack for a waterproof liner.

Maybe use it outside the bag as a waterproof rain cover.

CX.

Semi-inflate tie/tape closed improvised chair.. Or fill with styrofoam beads then close up. Also can make a hammock from them.. Just because theres an apocolypse doesnt mean you cant relax..

A garbage bag can be used to store a small amount of air,which can be drawn in through a plastic tube,for staying under water for longer than one can normally hold one's breath.

Scoop some air into it,put the tube into it by wrapping a rubber band around it,and stuff it up under your shirt,or let it float.

Keep in mind you can't go very deep,your respiratory muscles cannot counter water pressure beyond about 10 inches.

You can actually re-breathe the air from the bag for a time without having to hold your breath.

Be careful with this though,it can be dangerous.

Also.....

Since garbage bags are not particularly heavy,and can be very useful,I suppose they would be handy to have on hand as a barter item also,toilet paper too........