Serpentine belt: The back side of the serpentine belt has grooves like a tire. If they are cracked or worn you will want to replace it. Again, sooner than later applies. If you wait too long it will snap and break.
Fluids: Windshield wiper fluid made for cold weather is worth the little extra money. It contains a greater concentration of alcohol and less water, so it is less likely to freeze.
Check your antifreeze (also called coolant). Antifreeze is sold full strength and needs to be mixed with water. Check the container and it will tell you what to do. Coolant is sold already mixed and ready to be added.
You might want to consider an oil change if it hasn’t already been done. Be sure to keep your gas tank half full or more at all times to prevent a fuel line from freezing.