Water is a very important resource, especially when Hiking or on the battlefield, which you must have with you, at least in a half-liter flask.   

SBM thermos-has double walls with vacuum insulation, a threaded lid with a special chute that allows you to pour out the contents without unscrewing the lid completely, the lid itself can be used as a Cup. 

Lightweight and easy to carry. Two options for 0.4 and 0.5 liters.