here's what i carry whenever i fly. it's all legal as carry-on and if I survive the crash should keep me from becoming carrion.

emergency poncho
tube tent
emergency blanket
50ft 550 cord
Swedish flint
butane Bic lighter(legal again, horray! ^_^)
bandanna
large Nalgene bottle
steel cup fit on bottom of Nalgene
small PFAK. (band-aids, single sized advill, alka seltzer, pepcid, pepto, imodium, benadryl, week of Rx meds, gauze pads, med tape, small folding scissors)
Wild Cards (deck of playing cards printed with pics and descriptions of edible plants)
Howler whistle
2 pairs of extra socks
two pairs extra underwear
iPod
laptop
Inova X1 with one extra battery
dogtag in my boot
two good books

It all fits in the detachable pouch on my Breakaway Bag. The evil, terrorist aiding Leatherman and Altoids PSK are in the main pack with my clothes as Checked Luggage.
I've yet to be stopped for the Swedish flint. the steel striker for the flint could be sharpened on a rock, as could the stainless steel ID tag attached to my carry on. The blanket and tent would serve well for signaling as well as shelter. This is ETS so i won't go into the paracord.