I would love it if holding down the Shift Key while using the Pencil Tool draws straight lines. Basically holding down the Shift key temporarily changes the functionality of the Pencil Tool to the line tool.
The angle in which a user draws is based on the last direction the cursor was moving before the Shift Key was pressed.
Here’s an example of how Adobe Animate handles it as a point of reference. Not the best example, but a point of reference