Nalgene polythene bottles are not as tough as their Tritan counterparts, but they are cheaper and lighter. However they can make drinks taste "polytheney" and they are not so easy to clean.
They are leak proof and ideal for storing anything that needs to be kept dry or any non-corrosive liquid.
They also make good pee bottles (1 litre recommended!).
These bottles have a fixed on "loop top".
Two sizes: 500ml and 1 litre.