You never know what test day will bring. Rather than worry what will happen, plan for every contingency.
If you are taking the test remotely, test your equipment. Do what you can to ensure ideal test conditions: a quiet and well-lit space, stable internet connection and a nearby bathroom for test breaks. If you plan to eat or drink during the test break, lay out your refreshments ahead of time.
If you are taking the test outside your home, familiarize yourself with the route you will take to the test center. See if you can visit ahead of time to get a sense of the space. Pack what you will need to take, like identification, a sweater and a snack.