The Best Emergency Shelter is reusable and costs $1.50 at Walmart.
It is a plastic drop cloth that most buy when they paint a room of their house. I personally carry 4 of them.
I have been caught in many storms. I have slept through many storms under this simple piece of plastic. Rain storms come fast and furious. They come in sudden and unenduring duration. Winds are high and rip tents to pieces. These pieces of plastic are miracles. They wrap around you, your gear, cover the ground under you, cling to your body, and do not blow away. It clings itself to you. Throw it over you and go to sleep since you have nothing else better to do than ride it out.
You can also make a hole in it and use it as a Poncho, it also makes a good tent to sleep under and it wads up nicely as a reusable tent. It is the best $1.50 you will ever spend if you treat it decently.
It also makes a good covering over your sleeping bag to keeping the dew off your sleeping bag and other gear. As I mentioned in other posts ,using it in the diamond pattern is not as durable and I do not recommend this other than as an emergency fill in for the black plastic. I do not recommend using the black plastic for emergency shelter in HIGH WINDS due to its inflexibility. The black tarp has too much Sail Effect and you will be shelterless in high winds. Use the painters clear plastic in high wind emergency situations. Keeping the wind off you also adds warmth to your sleeping bag. Also keeping yourself, and your gear dry is very important. Having that set of dry clothes is an important relief when you are cold. Also having to spend a day drying clothes and equipment is a hassle when you want to be on the move. By the way, carrying wet equipment also adds a lot of weight to your gear and you will really be feeling it in your shoulders, back and legs.