Answer: Digital (or physical) Images & Your surroundings.
Explanation: You can use still photos as art inspiration, whether this is another persons art, a piece of clothing, people, animals etc,. These items will always be accessible to you and you are unable to misplace a digital image on a device. You can also use items around you for inspiration, like a marble table or countertop for a back drop on a art piece or for a real life portrait.