These are caravn-style 16W 12v lamps mounted in aluminium reflectors. They are generally used mounted to the stage side of each front of house speaker, often with coloured gel to mollify the otherwise bright white light. They can also be used on the ground as footlights, and aren't too heavy to hang from marquee sides, trees and the like.
Found as sets of three with a wimple sound-to-light controller, I have four sets of three that can be remotely controlled, connected using 5 pin DIN connectors. A simple controller box offers switched or sound to light options. These offer strongly coloured stage lighting, not very bright, but effective. Maplin are currently selling a similar set of six, the price dependent on whether they're having a sale or not...
Small AA battery powered chains or fairly lights make good decorative lighting for the stage, microphone stands, and if neecessary to outline marquee exits for night, and similar. Best bought in post-Christmas clearances.
Have a torch or headlamp or similar to hand - not only to illuminate the sound desk when dark, but to track cables around the back of the stage and the like. You may find a stalk-mounted map light for car use ideal to mount to the sound desk, too.
At an event in the middle of nowhere, people will look to you to provide lighting elsewhere too - either be very good at saying 'no', or have a few standalone lights available.