I was killing time in a West Marine the other day when i came across a nice survival addition, the Knot-a-Bag plastic bag refills from Davis, the weather station and sextant company. It's about $7 for 3 rolls.

Basically, it's exactly like the vegetable bags you get in the supermarket except stronger and each roll is only 1 1/2 by 3 inches and weighs less than 2 ounces. It is 10 meters of 8" diameter polyethylene bag material. You pull the plastic out of the center and cut it off and put a knot in the end to make a bag.

What can you use it for?
It's food suitable, so you can carry lots of water, berries etc and could use it as a transpiration bag over a leafy branch to get water.
It's very strong, almost as good as rope for tying things. Or you could use twisted strips of it as lashings for your shelter, or holding a dressing on etc.
If you spread it out, you can make a triangular bandage out of it to hold an arm.
A longish piece can be stuffed with non-pointy items and used as a billy bag over your shoulder.
It's flammable, will light from a flame but i can't start it with a ferro rod...
Since it's airtight, you could inflate one to use as a buoy to hold yourself up in water.
You can make a hat, or a brooch or a pterodactyl...

The only thing it's not really good for is shelter itself or weather protection, a trashbag would be a better choice. But you could still put lengths over your arms and legs and wrap some of it around yourself to keep wind and rain out. So it's useful and small enough to stow in my kit bags.

Interesting. Seems that if you have to tie a knot in each end, you are going to use a lot more material to make one bag than if is was sealed on one end tho...

Yesterday when I was shopping for my soon to arrive grandaughter I noticed a small container that fits on a keyring that holds a roll of plastic bags for things like diaper disposal and things like that. Only costs $2.50 so next time i'm in there I may get one and see how sturdy and how big the bags are.