What external light sources are at my disposal should I need?
When outside and wanting to light a subject or just fill shadows, use can be made of reflectors (various shapes and sizes) general rule being use silver for white skins and gold for black skins.
When sun is difficult or its late make use of an external flash, either on the camera or with the use of a trigger off camera and even better use with a soft box or umbrella on the flash.
External bigger light sources like the Elinchrom range can be used to great effect.
If power available continuous lighting such as red heads can be used.
In side use can be made of studio lights in studio or continuous lighting such as red heads to light a subject.
Use of a flash in place of studio lights also work well.
If moving about the only way one can shoot is with your flash attached to your camera and here use a diffuser to diffuse the power of your flash.