I would like to expand on what others have said. All were good points; IMHO.
Will all of you be carrying flashlights? If so do you have extra bulbs and batteries for each? Do you have a backup light? Same thing goes for all of the radios…extra batteries.
Carry a small notebook, 2 pens and a pencil. Make notes about what you see. As many have said it before, things do have a way of conking out. This is why you need 2 pens. The pencil comes in handy if all pens give out. Also log your “patrols.” It is easier to defend your notes in court than your memory. Write simple things down like, 0030—walked perimeter fence, locks secured (try them each time) etc. This looks good to the police and if you are called to court you won’t look dumb trying to recall if the padlock was locked or not.
Do you have a way to keep warm (or cool) dry and comfortable? Inside of a car with the heater on can be dangerous. The mention of comfortable shoes is extremely important advice. Standing or walking for hours in cowboy boots, for example, will become painful over time.
What provisions will you have for bathroom breaks? You may need an extra roll of TP in case what is provided runs out.
Keep hydrated, drinking fluids (avoid too much caffeine) aids the mind in keeping focused. Also if you are normally a diurnal person the sudden switching to nights will play hell on your body. Staying hydrated actually helps you make a better recovery.
If you have a small AM/FM radio, use it if your client says it is ok. I do not recommend an earphone, rather keep the volume low, but not so much as to not be heard. Change stations about every half-hour or so. Anyone hiding in the shadows will know you are awake and changing stations helps to prevent you from falling asleep.
Have a light snack in case you get hungry. Something like a cereal bar is far better than a full meal, which weighs you down.
Remember; security guards are thought of as fat, old, lazy and their routine is predictable. You want to be the complete opposite. Anything else you can do to vary “routine” will keep you unpredictable.
Good luck.
stargazer
Buried deep within each of us is a spark of greatness, a spark than can be fanned into flames of passion and achievement. That spark is not outside of you it is born deep within you.