I've been using silicone impregnated nylon (silnylon) tarps for backpacking for three years. I was astonished at how rugged they are considering how thin and light the material is. I couldn't make a hole bigger by pulling with two fingers with all my might.
It's almost the lightest, most compact tarp material you can get. Only spinnaker material is lighter.
However, it's not imune to burn holes from flying campfire sparks. And it is rather expensive.
So for a backpack BOB, where space and weight are at a premium, I think it's a good choice. You can also get silnylon ponchos that have been designed for use as roomy shelters.
http://www.trailquest.net/dlgcponchotarp.html
http://owareusa.com/
For a car trunk kit or for caching, you might want something that's less expensive, if not more resistant to fire. I'm talking about reinforced poly tarps here.
For flame resistance, I think you're back to canvas or ventile. Neither are stunningly light or compact, but if you intend to cook a lot with campfires, you might want the flame resistance of natural fibres.
Bear