The best drinking bottle ever made. If 0.5 liters were made into a so-called wide mouth version, that would be even better.
The best drinking bottle.
The large mouth makes cleaning easier. A clear measurement scale. Tight cap. Suitable volume. Nothing extra.
If you need some accessories, a cap on the attachment point (e.g. for a carabiner) and some kind of water purifier compatible with the bottle.
Nice basic bottle. The measuring scale is a handy addition.
Appropriately large, good cap.