I suggest:
Have a cache of things to practice.
For example, scales (with intervals if you're familiar with that concept), chords (and changing them fluently), songs (easy three chord ones), strumming technique, finger exercises such as you mentioned, playing with the
radio (even badly, just to get the strumming and chord changing into your 'things I am getting into my brainwaves'), single note melody, and rock star stances/gestures.
Then depending on your mood or sense of adventure or 'step backward' on one aspect, this gives you something else from which to choose for practicing, thus to save the day.