This thread has produced lots of good suggestions; I would only add that whatever you choose to carry, it would be worthwhile to set up your equipment and give it a trial run. Carry it and use your emergency shelter on a regular trip where you can move into something more substantial if necessary or set up in your backyard. If you ever need to use your rig, prior experience will be very helpful.
so true. i should for these bags i mentioned never having tried. problem is they're like Pandora's box: once opened they can never packed anywhere near as small again. if i were born a richer man, i'd've bought doubles of each and tested one set. so instead i take a chance they're as good as stated. i've been carrying them for 20 years and just hope i'll never need to depend on them. dumb, i know, so maybe you've pushed me to actually test 'em...