Obviously, you need a camera. What kind of camera is heavily debated and the topic of some of our other blogs (for example, this one). Ultimately a lot of that is going to come down to personal preference. There are a few minimum requirements, though. It should be something that has at least reasonable low light performance. There are going to be moments throughout the wedding day that you can’t add lighting, so you’ll need to be able to shoot in a higher ISO and know that you can at least recover the photo in post. This doesn’t mean that you need the best low light performance on the market, especially if you’re comfortable with a flash, but it does mean you’ll want a decent DSLR or mirrorless camera.
You’ll see in many posts that you absolutely have to have a camera with two card slots. I would put that in a nice to have category, but when you’re starting out I don’t think it’s an absolute necessity. Most wedding photographers started out with a camera with only one card slot because they couldn’t afford anything else. There are many very respected wedding photographers who are still shooting on a camera like the R, which is a very good camera but only has one card slot. Card failures do happen, and they can be really bad from a wedding day. But they are also becoming increasingly rare as technology improves. If you do shoot on a camera with only one card slot, I would recommend shooting on 32GB SD cards and switching them out fairly often. That way if one card fails, you only lose part of the wedding and not hte full wedding.
A backup camera is also nice to have as some extra comfort and is an absolute necessity when you get into higher price ranges, but when you’re just starting out I certainly wouldn’t tell you not to shoot a wedding just because you don’t have an extra camera body.