Very simple Sublime Text 3 package to add Sidebar options to open or clone files in a new vertical split.
As this is a very simple package intended for personal use, I have not considered adding it into Package Control.
To install, copy this folder to your Sublime Text Packages directory. You can find the path of this folder from the menu Preferences > Browse Packages....
You should see the new actions available from the sidebar after the folder has been moved there.