In certain Office apps that support it, such as Word & Outlook, I have “Show shortcut keys in screentips” enabled (right click on a toolbar, choose customize, and it's on the Options tab in certain of the apps). Normally, this displays the keyboard shortcut combinations (like Ctrl+Shift+B to bring up the address book in Outlook) when you hover over a toolbar button. But unfortunately it's not uniformly implemented, so in many cases there is a shortcut key for something but it's not listed in the tooltip.
Word, however, seems to be a little more rigorous about displaying the keyboard combinations, and I noticed today that Ctrl+Shift+F can be used to go to the font drop-down, and Ctrl+Shift+P to the font size drop-down, for Word, Excel & OneNote.
Word and Outlook also have Ctrl+] and Ctrl+[ (Ctrl+< or > also work) to change the font size on the fly, which I use all the time (only for HTML/RTF mail of course). A common task for me when creating a new Word doc is set up a title by: Ctrl+E, Ctrl+] a few times, type title, enter, Ctrl+L, Ctrl+[ a few times.