Professional photography equipment is heavy, there's no getting away that fact. Metal cases, mounts and barrels on the larger camera bodies and 'fast' lenses raise durability and quality but they also increase weight. By the time other equipment is factored in for a job (e.g. wide-angle lenses, telephotos, fish-eyes, strobes/flashes, radio triggers, batteries, light stands, modifiers, etc.), you can easily be looking at 10kg+ of equipment needing carried to create images.
Sometimes, I don’t need or want to take a lot of gear (even with an assistant) or I’m physically not able to. On such occasions, here is a list of 5 pieces of equipment I'll use when I need professional-quality images but I want to reduce the weight (e.g. I'm shooting someone on a hiking or biking expedition or the trekking stage of an adventure race);
Nikon D810 camera body - My main camera these days is a Nikon D4s for sports and a Nikon D810 for landscapes but, if I’m looking to reduce weight, I’ll happily take the D810 for sports (or, if the weather is poor, perhaps fall back on a D700 camera body I have used for a long time (I’m much less bothered about my D700 being ruined than I would be with my D810, even with camera insurance).
Nikon 16-35mm F4 lens - The lightest option I’d take would be a Nikon 24mm F2.8 lens (which works well with my older D700 camera bodies) but the high resolution of the D810 camera body is very unforgiving and I prefer newer solutions such as the 16-35mm F4 VR or 24-70mm F2.8 ED VR lenses. (My eyes always stray to my awesome Nikon 24mm F1.4 lens but having a versatility of a zoom trumps it when it’s a ‘one lens to do all’ day out).
Westcott 5-in-1 reflector - Not taking any lighting equipment means you're a slave to the ambient light, which isn't always ideal. If you plan to shoot environmental portraits, a 5-in-1 reflector is a lightweight alternative that enables you to, e.g. diffuse the light, fill in shadows or change the warmth of your shots to match the sunset. A Tri-grip reflector would be easier to hold but I find the original, collapsible models easier to pack.
Joby Ultrafit Sling Strap - A simple camera strap that screws into the bottom of the camera. It's easy to adjust and I find it comfier to use than the default camera straps. I wear it across my chest and it's long enough to cinch the camera down near my hip when I'm moving.
Zing Pro SLR neoprene case - I used one of these years ago on an expedition to the Southern Patagonian Ice Cap but it appears to have gone to that place things go where you're sure you've not thrown them out or sold them but you can't find them anymore. I recently purchased a new one and it's a really neat solution for protecting your camera against bumps and moisture, being a single piece of thick neoprene that you place your camera in and seal over the lens.
Exped Packsacks - AKA dry-bags. Professional cameras are fairly weatherproof but they're not invincible, as my frequent repair bills will testify to. Using the Zing camera case means my camera and lens is not as protected from the elements as, say, in the Lowepro Toploader Pro camera bag I usually carry outdoors. Placing the camera inside a dry bag inside my rucksack or camera backpack when I'm not using it gives me a really compact and weatherproof solution I have complete confidence in.
So there you have it. Six pieces of photography equipment I find useful when I want to travel light but still take professional-quality photos.
(Another option: Check out Nikon’s latest mirrorless cameras. Or perhaps Sony, whose full-frame camera bodies are lighter than Nikon or Canon’s. (I carry the Sony RX100 for outdoor photography when I’m not working for a client and I want to travel really light but still wish to capture decent quality images)