I open the Keyboard Shortcut menu far more often than I'd like to admit. How do I open this with a keyboard shortcut?
There doesn't appear to be an official keyboard shortcut built into Chrome for the Extensions menu. However, without using additional software, there are still ways to be able to access the menu relatively quickly.
You can add the Extensions menu as a bookmark on the bookmarks bar. Its URL is chrome://extensions/.
This puts it one click away. However, if you want to be able to access it from the keyboard only, there is another way. Right-click the Omnibar and choose "Edit search engines". Under "Other search engines", fill in the information as shown, and then choose Done.
This creates a "search engine" which can be accessed through the keyword 'ex'. Now, to access Extensions, you can press Ctrl+L to select the Omnibar, type
Since Extensions is a menu item in Chrome, you can assign it a keyboard shortcut through OS X's System Preferences.