My latest find is re-using bottles. Not a new idea here, but only recently did I consider that a free item could be better than the Platypus'(Platypii?) I paid high prices for.
The p.e.t.(polyethylene terephthalate) type designed for pressurized liquids are built stronger than non-pressurized bottles, and so, will last for dozens of usages. You can identify these 'rocket' bottles by the five pressure resistant flanges on the bottom; reminiscent of the bottom of an Apollo rocket. I like the one shown for Mitsuya Cider (34 grams in 500ml) because of its short and simple cylindrical shape.
I use various small sizes to carry alcohol for my stoves, down as small as 135ml.
These can not handle boiling liquids, but the next item can..
Re-using aluminum water bottles make an economical and dual-purpose water container because you can boil the water IN your carry bottle. 25 grams in 500ml for the one shown. One of these, an esbit and tray, and windscreen is a very light pot.
Either one are only slightly heavier than Platypus bottles, and unlike those floppy bottles, these can slide into pack side-pockets easily while only grasping the tops.
Having more than one water bottle allows for the safety of redundancy. It's unlikely more than one would rupture, even if your pack goes over a cliff. Three 500ml bottles allows for a system of 1:drinkable now, 2:for cooking(untreated), 3:treatting now with Micropur.
Other free items; can stoves, rubber bands replacing stuff sacks, bamboo hiking staff (280g).