For lunch, Au Premier is a good albeit expensive place to eat.
It is easily accessible, quiet, and overlooks the train station.
You can also just have an espresso.
For a quick sandwich, avoid the sandwich places on the main level and go downstairs. You get a better sandwich, typically for a better price. Don't overlook Sprüngli, which has some really good non-standard sandwiches. Try the white asparagus one!
I've found a working power supply accessible to the public
(maybe involuntarily) in the remote corner opposite Gleis 15/16,
in front of the snack bar, and right behind the lockers for SBB