Let me just put in a plug here for not trying to fill all of your so-called "dead time" with so-called "productive activity". Mind-wandering times like driving, showering, laundry, coffee-making, etc. can produce some of your most creative moments and may even be essential to your mental health. [0]

[0] https://www.sciencedirect.com/science/article/pii/S089662732...