Buying slave flashes are a good idea because they are commonly independently powered units that are usually in sync when your camera flashes. They use a power source of their own and are able to emit a burst of light whenever necessary. Many photographers use them by tying them up in places where light is needed and they will automatically react according to the situation. Placing them on a building or in areas a little back is also a good idea.
Knowing what other people use when applying portable flash units for a camera is a good idea to get a sense of what you should be using as well. There are many different varieties available but not all are good for what you may expect on the road. So choose carefully after proper consultation with other photographers and by looking on the internet for some useful information. Try to learn as much as possible about portable flash units for a camera.
Buying portable flash units is not necessary because you may need these lights for one specific scene. Not to mention, these portable flash units can be rather expensive depending on which type you are specifically looking for. There are a number of dealers that allow photographers to rent their portable flash units for a camera and charge a minimal fee as compared to the high cost of actually having to buy one. Getting expert advice on where the best rental places are is another good idea to get the best portable flash units for a camera without having to struggle by going to more than one place. Look for what meets your overall needs.