I'll be the first one to admit it, I'm a camera gear junkie. When I first started out many years ago I thought that you needed a ton of gear to get awesome results. Through the years I've learned its not the gear you have but the quality of light falling on your subject. Don't get me wrong the more lighting gear the better, but for on-location shoots with one model sometimes you get better results with minimal gear. Every photographer will eventually shoot on location and that is why it is essential to have a go to on location kit thats easily transportable. I use to bring tons of gear to on-location shoots such as elinchrom / alien bees studio strobes, beauty dishes, soft boxes, strip boxes, etc. But after a few dozen shoots, all this gear gets really heavy, really fast and sometimes isn't ideal for some locations. The solution? Create a mininalizt kit that will product great results and great quality of light, enjoy!
Canon 5D Mark III - Plain and simple you need this camera, its a beast
Westscott Rapid Box - The rapid box is a Octabox / beauty dish that delivers awesome results with either a small speed light or a medium strobe and is and compact when packed up. The perfect light modifyer for traveling to on-location shoots.
Flashpoint Streaklight 360 with power pack and triggers - This is a bare bulb flash which is the equivalent power of 6 speedlights. Use this as your Key light, the power can be conveniently be adjusted on camera with it proprietary trigger. The battery pack is also good for about 1800 full power flashes.
Youngnuo YN600rt speedlight - Do yourself a favor, pickup this cheap flash and leave your expensive speedlights at home, save them for when you shoot events. This flash is basically a copy of the $600 Canon 600RT speedlight. They run for about $100 on amazon and are great when you just need a flash for fill light. Plus if this flash goes over in the wind, you'll be happy it was your cheaper flash and not your expensive $600 speedlight.
Sekonic Litemaster Pro light meter - Most will argue if you necessary need a light meter? Well for dead on accurate exposure, I would recommend it.
Manfroto Nano Stand - This stand is a lightweight stand that is extremely compact when folded. While its not ideal for studio strobes, it does the job for speedlights.
White balance lens cap -Why do in post production what you can do in camera. Take a few minutes and dial in that white balance.
Memory cards -Always have plenty of memory cards on hand.