(I can see the letters are underlined when I click the toolbar button, but I'm not sure how to get to the toolbar from the keyboard -- Alt just takes me to the menu bar as usual)
Ctrl+0 sets the zoom level to "Zoom to page level".
Beyond that are the keyboard accelerators (the underlined characters in each item). To use them you simply open the menu and then press those letters for the sub-menus and the command you want to execute.
For example, to execute the Single Page View mode you press Alt+V (to open the View menu), then P (to open the Page Display sub-menu), then S (to select "Single Page View").