In the web application when reading an email there is an action menu for the email on the screen: "mark as read/unread, move to folder, move to trash, label, filter, etc.".

I would like to be able to choose some favorite labels and have them show up on this menu bar so I don't have to hunt for them in the label menu. Likewise you could use a simple algorithm to show the commonly used labels here as well. I have a lot of labels but tend to apply some frequently and don't have easy logic to be able to apply through the use of filters.

This feature could be viewport specific as I'm aware on smaller displays it might be harder to execute, but on my widescreen display I have so much real estate that could be used for a feature such as this.