Water in plastic water bottles seems to survive temperature extremes pretty well -- if you're concerned about chemicals leaching into your water you may want to do something different. All I do is cycle through it on a regular basis.

For food I keep my favorite road snacks (beef jerky) and Millennium bars on hand.

Clean water stored in clean containers in the dark stays good indefinitely. Exposure to light could create an environment for microorganisms to grow. With regard to a canteen, what kind of canteen is it?