Making it work could be as simple as a camera, and the desire to take as many photos as possible. Depending on how far you want to take your ideas, you could end up with a camera, battery grip, flash bracket, add-on flash with diffuser, a second camera, external wireless strobes, or a multitude of other things in your quest to take the best images you can.
Personally, I like to stay as light weight as possible and often take one or two camera bodies with lenses attached and that is it. With proper technique, almost any setup will be enough to result in quality output. On the other hand, framing, posing instructions, angles, post-processing, and overall feel of final images are attributes that uniquely develop in forming your own style of convention photography. I’ll try to give some insight on both aspects to further your development along or just start it off on a good foot.
When thinking about camera gear in relation to a convention setting, it is best to consider what type of photography you want to spend most of your time on. At least for me, the type of photography I do does have a big effect on what camera equipment I use.
When doing hall cosplay you will be walking around a lot, so a small camera and lens combination will probably suit you best. A small fully featured DSLR and fast large aperture zoom or prime lens would be a good choice. You might want to look at the lesser known brands as they tend to offer camera bodies that are smaller than standard sizes.
If you plan on having more private shoots compared to hall photography, having a larger more powerful camera setup might be a good idea, so you can maximize the quality of your final results. Taking things further, you could look into full-frame camera bodies, or even medium format if you have the funds available for such a purchase. When you don’t need to lug around camera gear for hours on end, it is possible and a lot more manageable to use specialty gear like that.