The 1 quart US issue canteen is probably one of the most ubiquitous military water bottles out there. The same stuff has been issued since the M-1956 load-bearing equipment came into use, and this is still going strong! These canteens are used, but still in perfectly serviceable condition.
This canteen is part of the US individual mess kit system. A metallic cup is available separately, which fits around the bottom of the canteen to save space in your pack. Even with the cup the canteen fits perfectly into the US army water canteen pouches, regardless of model (ALICE, MOLLE II, etc.).
Used and abused, but serviceable. Wash extremely well before use.
This canteen, coupled with the US canteen cup, is a combo that I have fallen in love with during an autumn march. This "canteen and cup" combination is nothing new - it's been in use by soldiers for years - but with my recent test, I myself understood just how useful this combination really is. Personally, I like to carry this combo in a pouch on my leg rig, along with an Esbit stove, fire-making tools, a spork, and a few food bars and instant soup pouches. With this setup you have everything you need to survive for a few days just in case, for example, your rucksack falls into some ravine, spontaneously explodes, or does something else not very beneficial to your situation. Cool stuff!
The canteen cup gives the added benefit of being able to heat stuff up when needed, which is extremely useful when in the wild. Also, the whole setup is quite compact and light, and you don't need to carry along any cookers or mess kits.
Arne