What about an engineered composite material like dyneema, or UHMWPE - Ultra High Molecular Weight Polyethylene as its called.. Given the fact that its used for radomes because its radar penetrable, I figure it would have a good side use as a car material as well. ;D
But no kidding, it's 40% stronger than Kevlar, 60% stronger than carbon or glass, 5 times as strong as polyamid/nylon and fifteen times stronger than steel, all compared by weight. Now we need a matrix.. if you could lay that up with a flexible (and thus cushioning) outer layer epoxy (bucket of G/F can you hear me?) with a non-destructive sandwich material that takes blows because its compressible (air? sponge?) before a harder inner layer with structural reinforcements on the inside, that could be something lightweight and able to take a beating.
Then, there is my all-time favorite, the air boat. Think rubber raft gone techy. Here's how it would work. If you have a sheet of airtight, coated textile that is connected to another sheet of textile with little strings (technically constructed similar to loop pile or real velvet before its cut, just waaay looser) this sandwich (closed at the edges, dooh) will become very stiff with a relatively small amount of air pressure in it. Still, a gas will compress, so catastrophic failure would be unlikely other than from very sharp items where they dont belong (unless we draw out our frind from above again, the UHMWPE

.
Now what do we have:
- Lightweight (most of it is air + no thick textiles needed in places where you don't need them)
- Holding shape (textile technology and some cleverly positioned ribs)
- Indestructible (maybe a replacable damage sheet on the underside would be a good idea?)
- pack-up for the hike in (reach places never before possible)
- cut your way out if pinned (in a waterfall, even.. very simple - could even re-fix it for the way out, woah)
- looking good, not your grandads raft this is! Shaped as any cboat, not ridiculous like some "blow up" kayaks we have seen..
- could include flotation for added weight savings
Well, the tech is here, but this would be such a crazy paradigm shift, really.. and hard to achieve at home and compared to the technology needed for this, an oven and aluminum forms suddenly look like childs toys. Maybe we have a chance once 3D-knitting technology is so widespread that you could basically just knit one out, coat it with whatever and blow it up ;D
Now lets take a look at proof of concept examples from the real world. Cam Brensinger is a smart guy from MIT who "invented" (not really, but he solved some hard-to-solve problems in the process) a blow-up tent and funded his company NEMO to bring you more of them.. -> he'd be cool to ask for lightweight beam technology
http://www.nemoequipment.com/airsupported_technology
Another part of the tech puzzle is well represented by the "Grace Table" by Phillipe Malouin, which utilises a probably quite standard raft floor material (yeah, its used for raft floors already...)
http://www.philippemalouin.com/grace.html
And to find a textile manufacturer that is capable of actually producing some of the stuff we'd need for that (they already do, albeit not in exactly the same specs, AFAIK) we have to look no further than these here guys:
http://www.contitech.de/pages/produkte/ ... en_en.html
.. well ok. Now for the shape. Any ideas?