When I worked for a studio the owner and I had a routine we'd go through before, during and after the wedding. I could describe our routine but it isn't important, and probably isn't even applicable today (different era, different media, different challenges). But my favorite part was the 8AM meet-up for breakfast, a haircut and shoeshine the morning of the event. Yes, it was a long time ago.
The important part is that you have a routine planned-out in advance. It might change as soon as you show up at the bride's house for her dressing shots, or you might stay true to plan right up to the last dance. Over time you will refine your routine and grow comfortable with it, and also comfortable when you have to deviate. Of course a part of that will be testing, cleaning and organizing all your gear and supplies the night before, making sure you have adequate spares for critical equipment and accessories, and double-checking that you have everything when you load up your car.
Besides photo gear bring a comb, hairbrush, small can of hairspray, shine control powder and make-up brush, a hand mirror, moist wipes, tissues, lots of bobby pins, small sewing kit with some buttons and several different size safety pins, peal-and-stick hemming tape and a lint roller, and keep several large umbrellas and some cleaning rags or paper towels in the car.
I am a very big proponent of visiting the church and reception venue in advance if you haven't been there before. Also, if you've agreed to shoot the formals and groups at a third location, scout that out as early as possible because often you will need a permit or reservation to shoot at parks, public gardens and the like.
Be sure to introduce yourself to the band leader, DJ, MC, Maitre D', or whomever is running the reception as soon as you arrive at the venue, so you can get on the same page for sequence and timing of the key activities and cues for each other to signal when to get ready and when you are done taking your shots.
Finally, being a good photographer and having the right gear is only part of the skills needed to successfully shoot weddings. You need to be well organized, work efficiently and stay in control of the environment while also being diplomatic with the couple, their family and their guests.