I have been working with two types of spinnaker as well as 2 weights of cuben
fiber and lots of silicone type 66 nylon parachute and the old standyby urethane
ripstop nylon. The spinnaker cloth saves a tiny bit of weight over the silcone
coated nylon which in turn is half the weight of regular 1.9 oz urethane ripstop.
The cuben fiber is the lightest of the bunch. The spinnakers and cuben are a bit
fragil, but if you take great pains to be careful in settup, they can last many
days. The standard 1.1 oz silicone coated nylon has proven itself to last as
well as 1.9 oz urethane in most circumstances. The type 66 of nylon is a bit
stronger than regular type 6 nylon and the silicone coating can double or triple
the tear strength of the fabric. Many of the lighter fabrics are not flame retardent,
so if part of your survival plan involves a fire, keep that in mind.

I like to bring a 6x8 silnylon tarp in my pack for ski SAR stuff, some of my
team buddies bring a silnylon poncho or a silnylon bivy. A large tarp
can make a reasonable lunch shelter even without trees in the snow. Dig
a hole for everyone's feet, pull the tarp over your heads with everyone
facing and tuck the tarp under your butts. Good wind break on a ski trip.
Doug has used some of the silnylon tarps for his airplane kits.