A clear, half-liter or gallon plastic container that would normally hold milk, orange juice, or chocolate milk, is converted to a reusable water jug.
John: "Hey dude, can I have some of your gatorade?"
Ryan: "Hey man, I'm sick of your bullshit. Get your own!"
John: "Woah, okay dude, chill out dick munch."
(Thus John is too cheap to buy gatorade in bulk and converts half-liter orange juice to water jug)
({ Next day at Practice)
Ryan: "Hey John, forgot my gatorade. Can I have some?"
John: (Has more than enough water) "Fuck off faggot!"
...Thus Poor Fellow's Canteen was born