In reply to Lupine Lacuna:
im a huge fan of those thin bottles some mineral water comes in (in japan the water is ilohas, maybe different there). its still plastic, but you can squish it down to about 1/4 the size when done, or half fill them and squeeze the air out so they sit flat.
the rigidity of a real bottle but the packability of a camelback.
will last a few trips and as an added bonus come with water in them!
also brilliant piss bottles.