I recently came across a great product--Vapur collapsible plastic bottles. When empty, you can roll them up or store them flat. They weigh practically nothing and tuck into most any Tom Bihn bag. They're BPA free and made in the USA. Also, the company seems like the kind of place I like to support, donating 1% to projects dedicated to world water issues. Right now they're involved in a clean water for Haiti project.
So, if you like packing light and are looking for a reusable, washable, lightweight bottle that packs easily anywhere, give this link a look: https://vapur.us/