If something is habitual, it's what you usually do. Your habitual jeans and t-shirt might work for school, but try dressing up for the opera.
Habitual is the adjective form of habit, which comes from the Latin habēre, which meant the mode of one's being, and often referred to the mode of dress. Now habit means anything you do repeatedly — your habitual actions. Perhaps you have a habitual preference for cheeseburgers, which you eat at your habitual restaurant on your habitual Wednesday night out.