Hefty trash compactor liners make very good pack liners, only weigh a couple of oz's and are pretty sturdy. They can be used in pinch for a ground cloth (have to be cut). They can used to collect water. They also make a great door for a debris shelter- in the summer w/ leaves/litter/other insulated material, in the winter fill w/ snow. Lots and lots of other uses- a true multi use item 
