For landscapes and even portraits, I use the combination of the Canon 5D Mark III wth the Canon 17-40mm f/4 L lens. Alot of photographers may not consider this to be a lens for portraits but I have created some interesting wide angle portrait images with this lens. It may not have a wide aperture compared to the more expensive prime lenses but still I personally feel that this is a good lens for portraits.
Regarding accessories, I have a number of batteries, flashgun (Canon 430 EX II), transmitter and receiver for flashgun if wanting to use off-camera flash, remote shutter release, Kirk BL-5DMarkIII L-bracket, filters ( ND1000, Polarizer), Mefoto Globetrotter tripod, wildlife watching bag hide, wildlife watching bean bag, lens cleaning kit, calculator, battery chargers for Canon and 9V/AA/AAA batteries. The bean bag is useful for getting down to eye level if shooting wildlife because it adds a good level of stability. The L-bracket is useful if one would quickly mount the camera on a tripod from landscape to portrait orientation instead of having to use the ballhead to achieve this. The disadvantage of using the ballhead for this purpose is that it takes time and it may not be able to support the weight of the camera when trying to shoot in portrait orientation.
Now with camera bags, I have two bags by Mindshift which is a sub brand of Think Tank. The Mindshift Trailscape 18L and the Mindshift Backlight 36L. The Backlight 36L one has alot of storage and can also accomodate a 15″ laptop plus 11L of personal gear like a jacket etc in the front pockets. Both camera bags are great for the outdoors and I feel the Backlight 36L can be used for a multi day trek in the Himalayas and I also use this bag when I have to carry all my gear on photographic holidays so this way I can get some good portraits, wildlife and landscape shots. With everything in the bag, it weighs just under 15kg.
I use the smaller Trailscape 18L bag for simple day trips or small assignments or even a walk in the park because carrying the bigger bag would be impractical and unnecessary weight.