I just got back from traveling over the holidays and wanted to share a new travel goodie with you. It's a Platypus collapsible water bottle. I have the .5L/17oz. size., and as you can see, when it's full of water, it is (roughly) the shape of a normal water bottle. When it's empty, it's completely flat and can be folded or rolled up on itself to stash in a pocket or a handbag.
One thing I was afraid of is that it would be easy to squeeze the bottle too hard and spill water all over the place. That doesn't happen because, apparently, the plastic is some magically perfect balance of rugged and supple. It will hold it's shape when you're drinking out of it, yet it will squish around to fit whatever space is available in your bag. It hasn't leaked a drop, and will stand up like a normal bottle even if it's only partially filled with water.
I'm used to carrying a larger (27 ounce) bottle as my everyday water bottle, so it does seem a bit on the small side. Still, 17 ounces is plenty to get you from one water fountain to the next if you're just running around town or in and out of airports. Water is actually pretty heavy to carry, so if you're really trying to cut down on how much you're dragging around, it's worth the extra refill stops. Overall, it's a good size for traveling, and a real bargain at only $8!