This is my list of essential travel gear.
Cell Phone with a good camera and good GPS - I use and highly recommend the Samsung Galaxy S9 phone. It has an excellent camera which takes very clear and detailed photos in any light. The zoom creates pixelated photos so a DSLR camera with a zoom lens is better for zooming. Almost all of the photos on the web site were taken with this camera.
Spare cell phone instead of a battery bank - I use an extra cell phone instead of a portable battery pack because I always have a few laying around and they are about the same size and weight for packing. An extra phone or battery is essential for those long travel days when you need the phone to find your way around when you arrive but you also want to listen to music all day while travelling.
Digital SLR camera with zoom lens - I currently use a Canon EOS 1100D camera with a Tamron 18-200 MM lens. I'm not happy with it because it is so hard to get clear zoom and low light shots. The non-zoomed and low-light photos with the Galaxy S9 are so much better than the Canon.
LifeStraw Water Purifier - For those places where you don't want to drink the water, the LifeStraw is a life saver. It is very lightweight for packing but it is a little hard to use because you have to suck the water through a thick filter. These are easy to find at Amazon, Walmart and Target. For long or multi-day hikes this is useful because if there is water available in rivers, etc. then you won't have to carry so much water. I have also used it in sketchy places like India for brushing my teeth and making coffee when I run out of bottled water.
Zip off pants with zipper pockets - This is my favorite clothing item since they work as shorts or long pants. The zipper pockets are essential to keep your valuables safe on crowded trains and to keep stuff from falling out of your pockets when reclining or laying down. They are lightweight and dry very quickly so I also use them as a swimsuit. With two pair of these, I don't need to carry any other pants, shorts, or a swimsuit.