The up/down keys were added in #83696 to allow navigation of Autocomplete options. However, there seem to be a few more keyboard shortcuts we could add. The web's select tag allows page up/down and ctrl + arrow (try it here). We should probably support the same.

It seems to me (on Mac Chrome) that page up/down and ctrl/option + up/down all jump to the beginning/end of the list, so no fancy concept of pages is necessary.