Here's the gear I can bring to a shoot and generally do :
- camera body : Canon 50 D
- lenses : EF-S 10-22/3.5-4.5, EF 35/2.0, EF 50/1.4, EF 24-105/4 L
- Canon EX 430 speedlight + batteries
- radio transmitter (from my studio kit) + reciever
- Strobist gel kit
- a roll of gaffer tape
- tripod + umbrella kit for the strobe
- tripod for camera
Sometimes a friend will act as an assistant and bring a second strobe with his own reciever (we use the same brand). It is useful to have two strobes, but not mandatory. When shooting on location, you can almost always use available light as a secondary light source.
I don't have a reflector. The problem with reflectors is that your either have someone hold it, or have to bring another tripod to hold it (holding it myself is not a solution, I shoot full body a lot). If I have an assistant, I'll use a secondary strobe for fill. If I'm alone I don't want to carry the extra gear.
During the shoot, I rarely use all of this. I choose a lens at the beginning of the shoot and stick with it (keeps style and colors consistent). If there's enough natural light, the strobe stays in my bag. I try to keep things as simple as possible while shooting, and focus a lot more on my communication with the cosplayer, rather than on technicalities (even if I can and will spend time to get the shots I want).
The best shoot I've done last year, I only used my body and 50 mm prime, and NOTHING else. The place was a gorgeous park, it was a spring afternoon and the light was simply beautiful. I didn't need more than that, and this kind of setup allows for more mobility.
If I have specific ideas about the shoot, photos I know I'll make, I can also bring small accessories (or ask the cosplayer(s) to bring them).