1. Black Velvet
This light absorbing material has a veritable myriad of applications, from using it purely as a backdrop, flagging unwanted flare or even blacking out windows on location, this material loves to suck up unwanted light from your setup. Black velvet is a thick fabric that resembles fine fur. Its dense structure means light hits the fabric gets bounced around in the weave and reflects very little light back out, anybody who has ever photographed pets with black fur will have experienced a similar effect. It comes in many forms so be sure to get the denser crushed velvet with a high cotton content, taking care to avoid the cheaper thinner fabric which contains more synthetic properties making it next to useless as it appears very shiny under direct light.
2. Baby oil
Although at first this might seem a little odd, a little bottle of this in your bag could give your shots an edge, literally. Apart from the obvious useful applications, baby oil added liberally to skin, especially if you are photographing tattoos, can give the model's skin and ink a new lease of life. Tattoos appear fresh and brand new as the 'wet-look' appearance darkens down the colours giving them a more defined look.
Plus if you are somebody who likes to integrate a more structured look to you're images by using edge lighting or back lighting, baby oil can help the model to stand out from the background. Whether it be on location or in the studio, baby oil applied to the model's exposed skin will give a very shiny look allowing those secondary lighting effects to have extra punch, really enhancing the edge transitions therefore allowing for strong shapes to be formed by the highlights.
3. Black gaffer tape
This is not to be confused with duct tape, the shiny silver tape which has a habit of bouncing light strangely if used in the wrong places. Gaffer tape needs little introduction but for those who are unfamiliar with this universal crisis delayer it is a cotton cloth tape with very strong adhesive properties. Another major difference and benefit of using gaffer tape over duct tape is that it doesn't leave a sticky residue behind, this can be crucial especially where expensive equipment is concerned as well as not leaving a mark when you vacate a location. I'm sure we have all been in situations where we wished we had it so get it in your photo bag now, don't wait until the next time you want to stick a flashgun to the wall and wished you had some.
This might seem an obvious one to those location photographers out there but to studio shooters it can sometimes be overlooked as a useful tool when we have so many lighting modifiers at our disposal. Reflectors come in a myriad of shapes and sizes and choosing the right one will obviously depended on the job at hand. That being said it is easy to say that location shooters will want a 6ft scrim/reflector but their is no point in getting one if you are never going to be bothered to take it out with you. Be realistic with your limitations and get a reflector size the suits your mobility too.
Reflectors also come in many different forms, so it's worth bearing this in mind if your only going to be packing a 'one size fits all' approach. Some basic reflectors are just silver light bouncers whereas others can be converted into several different types and with them being so lightweight and reasonably priced there seems little reason not to get a convertible one, these usually consist of a silver and gold reflector casing with a black and white disk inside. They can also come with translucent gauze material disk inside, commonly known as a scrim. These are incredibly useful at softening/diffusing harsh light like the sun on location but it can also double as a quick softbox for strobes and flashguns in a studio. The silver reflector usually bounces light directly with little loss of exposure whereas the white bounce will normally loose a stop (half the amount of light), this is of course a crude estimation and is based on the reflector being only a few feet from the model. This idea can be useful though if you have the sun behind the model and want to bounce some light back onto the face, as long as you are exposing for the subject l this will give your background a nice brightly exposed backdrop. The gold side here will give the model a warm sun-kissed feel similar to a sunset shot. Bear in mind of course that all these techniques work in a studio too and although a reflector may not be quite as accurate and modifiable as a strobe they are incredibly quick to use and once you are familiar with your particular reflector you can quickly adapt to a lighting problem as the situation demands it. If all else fails you can even use your reflector as a makeshift fan and give those windswept hair shots a try.
5. Spare sync cable
This has saved my dignity on more than one occasion, when all the all hi-tech gimmickry fails there is nothing that will let you down about a good old fashioned physical connection from camera to flash. Shooting in a studio is one thing but on location you don't know what the situation will throw at you. Anything from high voltage interference with radio triggers to trying to bounce your infa-red slaves around corners to the back lights. I've sculpted 'light-catching' cups out of tinfoil before now and fixed them to the tops of my strobes receivers to get them to fire remotely, and although this worked all I would of needed was a spare sync cable. They weigh next to nothing, take up hardly any room and are incredibly cheap.