I use Git Bash a lot in addition to the git tools integrated into Visual Studio, and found a way to launch it with a hot key combination within Visual Studio.

In the Visual Studio Menu Bar navigate to the following:
Tools -> External Tools -> Add New

Enter these values:
Name: Git Bash
Command: C:\Program Files\Git\git-bash.exe
Initial Dir : $(SolutionDir)

 

Now you should see the new option show up in the external tools section.

 

To add a keyboard shortcut navigate to the following:
Tools -> Options -> Environment -> Keyboard
Search for “Tools.ExternalCommand[X]”, where X is the position of the Git Bash command in the external tools menu.

 

You may have to restart visual studio after creating the external tool, or the keyboard shortcut assignment.

Ryan