The most frustrating thing is to have the desire to create something but come up flat for ideas. As mentioned it's best to step away since (my) muse occasionally needs personal time. This is usually a great time for spring cleaning - it's a mindless activity which provides great solutions to long-standing problems. If nothing more, you get a clean house out of the deal, which can also be inspirational.

I'll also take the time to catch up on research, maybe lighting, composition or trying to decipher what f-stop does in 3D software. Just got back from a road trip (visited Pixar among other things) filled with many colorful stories. Gardening. Sitting in a quiet room listening to my thoughts.