One feature often under-utilized in OneNote is the Lasso tool. On the Surface Pro, there are a few different ways to execute this feature since you have mouse, pen, and touch as options. See my video below for a demo, but here are the details:
OneNote Desktop: Pen, Finger, or the Lasso Select button in the Draw toolbar. You can use the mouse to lasso or just select things with a basic square selector, but lasso is more precise (curves can go around other objects)
OneNote Modern UI app: Pen or Finger – no Lasso Select button (although Lasso options will show in the radial menu after you lasso something).