Insulated Water Bottle. Ozark Trail Brand, 64 oz. Bought at WallyWorld. Not exactly transformative, since I have a couple other ones from different companies, well used, well liked for many camp chores, etc. Used mainly during my hard water travels and winter camping. Good quality, nice size stopper, holds heat or cold fairly well, probably as good as what I have similar in concept from Keen, RTic brands. It could even be a canteen for a large group.
It's biggest downside is bulk and weight, but we have found it to be a positive addition to our camping kit. You wouldn't want to portage it except in a group, given it's weight, weight when filled. (darn, can't someone invent water 'lite'...taste great, less heavy?!).
Oh, why it was top of my list? Bought two, each $16 or so, gave one to my son who used it for a weeks backcountry camping this late winter, praised it as being highly useful during their trip. We got probably a weeks use out of it too and put it to good use on a BSA scout outing...lots of hot chocolate got made from one container, no worries about constantly firing up the stove (flames and teenagers, not always a good combination) then doubled down as hot water to help clean up cups an hour or so later with another refill of hot water.