nothing is required... except maybe a ballcap... those seem pretty standard issue for pmc loadouts.
The best way to make a contractor loadout is the same way they make them.
First, make a list of how you would like it to function.
i.e. Do you need an armor carrier? Do you have to hold 25mags or just 3? What kind of mags? How many of those mags and what kind of mags do you need accessibly immediately, and how are you most comfortable accessing them in the situations you will need them? Do you need a hydration carrier or do you prefer canteens and water bottles? Do you prefer to draw your secondary from a vest, belt, shoulder holster, or drop-leg? Plan accordingly. Do you have a com system? Do you need a spot for random items, or do your pants' cargo pockets work well enough for you? Kneepads? some people don't like them... some people love them
Now, look at that list and rank your priorities, leave a blank line at the top. Now add one more item to the list. Can I wear this all day comfortably? <--Put that one at the top of the list.
That's how you make the loadout. Comfort + Function, without worrying about form. To pull off the 'look', just avoid camo, and don't try to look like rambo... the biggest part of the look once you don't have camo (and you have a noticable amount of gear) is your attitude, this is one of the reasons that comfort is so important. If you are fighting your gear or are uncomfortable in it, you will NEVER pull off a contractor look.
What I do:
Neutral colored abercrombie t-shirts (very comfortable and soft.
) under an RRV, with a foliage shemagh and tan ballcap... grayish brown gloves, desert boots and tactical cargo pants (I LOVE and highly recommend LAPG Operator pants for anyone looking for tac pants). I keep my pistol in a leg rig and carry as much ammo as I need for the mission at hand, or collapse pockets for a lighter weight approach. I can also drop down to a pistols-only loadout easily by switching the RRV to a camelbak and using my leg-rig to carry extra pistol mags (I have a dump pouch on my pistol-belt). It is extremely comfortable and looks the part of PMC. YMMV. PMC is all about customization and just making something that is comfortable and effective first, and worrying about looks after the killing is done.