Alternative automotive uses for surplus 80% alcohol hand sanitizer?

Cut it with water 50/50 and put some on your windshield. See if it wipes off easily. As mentioned above, it would be a good windshield cleaner. Peroxide is a great oxidizer. I would be careful cleaning interior surfaces with it. If testing on an inconspicuous spot shows no damage, then you might use it for cleaning seats, interior doors, and the dashboard.