Coca-Cola PET Coke bottle (empty)

An empty Coca-Cola PET bottle is a textbook example of ultralight use-what-you-have thinking — an ordinary 0.5 L soda bottle with a standard 28mm PCO thread that screws directly onto Sawyer Squeeze or Platypus filters with no adapter needed. It weighs around 48 g, lighter than most purpose-built outdoor bottles of similar capacity, and it's food-grade plastic that's BPA free. The cost is effectively zero if you're reusing a bottle instead of recycling it. The trade-offs are obvious: no carry loop, no hot-liquid tolerance, and no guarantee of long-term durability — thin-walled PET degrades faster than HDPE or Nalgene, cracks with repeated squeezing, and gets brittle under UV exposure over time. For short trips, or as a backup bottle in a filter setup, it's an unbeatably light and cheap option; for long thru-hikes where a bottle has to survive weeks of rough handling, experienced ultralight hikers tend to swap it out periodically, since a replacement costs about as much as the drink itself.