Lenses
I usually pair two focal lengths together. I tend to go with either 24mm & 50mm or 35mm & 85mm as complementary focal lenghts. The gaps in between standard focal lengths are redundant I find, so prime lenses are usually my go to choice. You could go with a 24-70mm or similar zoom lens, but I'd rather have the faster apertures and lighter weight of a prime. Usually, I only keep one prime on the camera (35mm or 50mm) and keep the other lens in the bag. I rarely switch them during any given day, unless I really need a different field of view. There are "travel zooms", like a 24-200mm zoom, but I've never seen one that I liked. You usually trade image quality for reach, and that is normally not a compromise I'm willing to make.
Unless you are sure you need a long telephoto lens, I usually recommend leaving the longer focal lengths at home. Good telephoto zooms or primes tend to be heavy, and I've rarely used one when I bothered to drag it along. If you are sure you need it (for wildlife or sports for instance), longer is nearly always better. I'd recommend at least something in the 600mm range for birds and wildlife, so usually your choice will be a 150-600 zoom, or a fast 300mm prime with a 1.4x or 2x teleconverter. I find the 70-200 lenses usually too cumbersome for travel, and you can always take a nice portrait with a 50mm or 85mm anyway, as long as you get a few steps closer to the subject.
Narrowing down the options to one or two focal lengths, helps focus more on subject, scene and composition. It doesn't matter if you can't get every possible shot. What usually happens is you'd either miss the moment while contemplating what lens and gear to use, or you'd never even experience the moment because you got tired from hauling everything around all day. The point is to enjoy yourself, as soon as that happens, the shots will follow. No matter what gear you happen to carry at the time. The more you use a single focal length, the more you will get used to seeing the frame without even raising the camera to your eye.
Accessories
As little as possible. I usually only bring the following and anything else I brought stays in the safe at the hotel.
- One or two extra batteries, just enough to last the day. I've never used up more than two batteries on any given day with my Fujifilm cameras. But I keep the camera switched off untiI I see something. By the time I've raised it to my eye, it's on again anyway. For film cameras, one spare battery of whatever type they use.
- A lens pen. Just in case I really messed up my front element or filter. I don't even bother with the occasional dust specks until it gets really dirty. Cura Lens Cleaner & Wipes works even better if you can find it, they have tiny travel sized kits. And those are better for old film cameras and lenses.
- My phone. I use offline maps a lot to navigate a city and mark interesting places beforehand. I never bother with paper maps anymore. Also, how else will you capture those pesky Pokémon?
- My ID, a debit card, a credit card, some cash. Maybe a public transport card, like Oyster. Everthing else stays in my wallet in the safe. I keep the cards and money in my front pocket.
- A small hex key to unlock an Arca Swiss plate, if I'm using one (like for the Peak Design Capture Pro clip).
- Sometimes, I bring a battery pack to charge the phone, since it's battery life is just plain bad. As an added bonus, the battery pack is also compatible with the Fujifilm X100T and hopefully also the X-T2 via the built-in usb micro port.
- Depending on the weather, some sunblock in a small tube.
- If you shoot film, two or three extra rolls tops.