Carry a spare battery for your camcorder. If you anticipate shooting a bunch, you may want to carry more than one spare.
Amazingly, most Mini-DV camcorders do not include a FireWire cable. You will have to buy your own. Make sure you buy the cable with the correct connectors.
Most camcorders have a threaded end where you can attach different lenses. A UV lens will block UV rays from getting into your video, but that is not the real reason you want to attach it to your camcorder. It's a clear lens that sits in front of the real lens, so you can think of it as an inexpensive sacrificial lamb.
Use this to blow dust off of your equipment, especially from the lens of the camcorder.
A big towel may seem like a strange thing to carry around, but it has many uses. You can wipe your hands and face with it. In many cases, you have to lay your camcorder on a hard and dirty surface. With the towel handy, just lay your camcorder on top of it. The towel will also dampen any vibration.
Use this brightly colored tape to secure wires on the floor. You don't want to get sued by people tripping over your wires.
After editing a few videos, you will realize that the mouse/keyboard combination really slows things down. Keyboard combos will interrupt your workflow and slow production. A programmable secondary controller for your other hand will make you a much happier person. You can check out our review of the Contour Design Shuttle Pro 2 controller.
Always carry a knife or multitool with a knife to cut things. You will also want to protect your expensive equipment.
You don't expect to plug your $3,000 camera straight into a socket do you?
You will need to carry all this stuff around, so it only makes sense to wear a camera vest. You don't have to buy an actual camera vest because any fishing and multi-pocketed vest will work.