Does anyone else here keep Bottles from Drinks like Gatorade or Powerade as spare/lightweight Canteens?
Yep. I use one as my powdered drink mix container. My Playtpus bladders get filled only with clear water. They are definitely durable enough for hiking and far better than the very lightweight ordinary water bottles but obviously they aren't as durable as a Nalgene wide-mouth which I will use for car camping and kayaking.