If you plan to use a shower curtain that has been used in the traditional way as a shower curtain you will want to get rid of any mildew and hard water deposits on the curtain before packing away. One simple way is to lay the curtain out flat and spray with undiluted white vinegar. Let the vinegar work for 30 minutes and then rinse well with water, and hang to dry. You do not want to roll or fold up a plastic curtain with mildew on it and then stick it in your pack.
Most standard shower curtains are more or less 72 by 72 inches. The plastic is heavy enough to sew/stitch together, and yet can be easily fitted to objects such as your body.
Drape the shower curtain over your head and shoulders with the grommet side to the ground. It would be good to have a magic marker handy at this point. Put a dot on the plastic where it touches each shoulder. Remove the curtain and put a small piece of duct tape over the dot on each side of the plastic.
You will put a hole through each piece of tape. The tape helps to keeps the holes from expanding. Next, cut two pieces of cordage and knot one end of each piece and then thread a piece through both holes. Put the emergency poncho back over your head and shoulders and tie off the pieces of cordage to hold the ad hoc poncho in place. You can from this point repeat the process so you can tie off the poncho to hold the hood in place and to pull the poncho together further down your body. Tie off under the chin for the hood, but keep in mind you do not want to create a choking hazard.
Another method would be to cut a piece out of the center that your head would fit through and simply wear that way, but your head would be unprotected and water will easily drip through the opening. Use duct tape around the edges of any holes you cut to keep the plastic from tearing.
Two shower curtains can be connected using the grommets to create a shelter. Use as you would any nylon or canvas tarp. Clear shower curtains would create the same effects as a greenhouse, so for cold weather shelters, this would be ideal if there is sunshine to warm the plastic, and thus, radiate heat to your body during the day. For nighttime, you could cover the shelter with pine boughs, pine needles, grasses, leaves or any vegetation to reduce the heat conduction from inside the shelter.
Once again use duct tape to harden any holes you put in the plastic. You may have to use cordage along the bottom to secure to limbs or ground stakes, and so you do not want the plastic tearing.
Warm the Inside of Your Vehicle by Securing the Curtain over the Front Windshield
Tape the curtain so it catches the sun if you are stranded in your vehicle. This will create a greenhouse effect and increase the temperature inside the car during the daylight hours. At night, you would reverse the process by using Mylar emergency blankets to reflect heat back into the vehicle.
Make Shift Greenhouse
You can take supple saplings, or any flexible plastic or other material to create a rounded greenhouse. Anchor one end to the ground and then bend over the sapling or PVC and secure the other end in the ground to create a half hoop. Drape the plastic over the hoops and secure. This would be a very small greenhouse but it can be used in the daylight hours to give your plants the much-needed sunshine, while still being protected in cold weather. You would likely have to protect the plants at night by moving them indoors or use some other means.
Waterproof Sleeping Bag Cover
Fit and cut the plastic to size making sure you do not cut the grommets off. Use the grommets so you do not have to cut so many holes in the plastic to secure together. Once cut to size stitch together using cordage or use duct tape for a more temporary cover.
Make a Water Bladder Using a Straw and a Piece of Shower Curtain
You would simply cut a round piece and tie off as if you were making a typical sachet but, this time, put a straw in the center as you tie off so you can drink from the bladder and then refill the bladder. You obviously cannot tip the bladder over but you can secure it so it can be carried over your shoulder or hung on your pack.
Collect Rain or Morning Dew
Make a depression in the ground and cover with the plastic to create a cup to collect rain or dew. You can also drape the plastic over vegetation or rocks, but you will need to create small depressions in the plastic for the moisture to collect in.
The uses for plastic during a survival situation are virtually endless. With a little imagination, you can come up with even more uses for a plastic shower curtain.