My standard adventure travel kit would include things from the list below selected for the climate of the destination. If I have the down jacket and warmer shoes, it is an infinite travel kit suitable for pretty much all habitable climate zones.
La Sportiva Akasha II Trail Running Shoes
My go-to travel shoes. They look somewhat dorky, but they are light, stable, breathable, and have very good grip, especially on wet surfaces (better than many hiking boots). They are not racing running shoes, so they have enough cushioning and flexibility for all-day comfort. Suitable for anything from cities to hikes anywhere above 5°C where it’s not pouring rain, as they are not Gore-Tex. When it’s warm, even when they get wet, they drain and dry very fast. No Gore-Tex seems to be a more versatile choice, especially for warm climates. If it’s colder and potentially wet, I would take something similar but with Gore-Tex, or hiking boots if it is seriously cold and snowy.
Montbell Slip-On Sandals (Flip Flops)
When it is very hot, a beach day, or even lots of religious places where I have to remove footwear, flip flops are indispensable. This pair by the Japanese brand Montbell is by far the most comfortable flip flops I have tried. Grippy, with many points of contact with the foot. The only negatives are that they are expensive outside of Japan, and they don’t dry super fast when they get wet due to some textile parts.
Merino Wool Socks
I have an assortment of merino socks from Smartwool, Darn Tough, and Point6 ranging from very thin to extra heavy for -30°C. At least one medium-weight pair is a must as they last for years, they barely stink, and have very efficient thermal regulation properties. Even for warm climates, I would have one pair for flights and some unplanned cold episodes. For very thin sports socks, merino is not as optimal as it gets a bit hot; in that case, I use synthetic sports socks. But they do go stinky fast
Marmot Hiking Pants
Super-light stretchable material. Not waterproof, but dries fast. For extra warmth, I prefer a merino base layer bottom instead of heavier material pants, which add more flexibility in different temperatures.
Fake Kathmandu Shorts From Kathmandu
I used to wear convertible Quechua pants, but the fit was bad, and they look incredibly bad. So to experiment, I purchased some fake Kathmandu shorts in Kathmandu (Nepal). The material is exceptionally light and stretchy, thus very comfortable. They had some pocket zip issues that had to be fixed, but otherwise, I am very happy, go buy the real thing!
Montbell Merino Wool Underwear
I have 5 pairs of those, they are fantastic for hot and cold climates alike – somehow cold and warm at the same time. They do not get stinky (at least from the bacteria), so you can get way by washing them a bit less often. But, obviously, you still need to wash them, but that is alright as they are very thin and dry very fast. But they are expensive outside of Japan.
I have experimented with all kinds of underwear and merino still comes on top for travel. Synthetic is good for sport, but gets very stinky very fast, might cause rashes; cotton is good for general use and comfort, but still gets stinky, does not dry as fast and is a bit heavier.
Merino Wool T-shirt
For 10-25°C temps, I would bring a merino T-shirt. When it’s hotter than that, merino is too hot. Otherwise, it is very versatile, stays fresh for long. Thermowave, Devold, and Icebreaker have a solid options.
Merino Base Layer
If the temps will be dropping below 0°C, I would bring a merino base layer top, if the trip involves camping or temps below -10°C I will bring a bottom as well. In terms of weight, it is one of the most efficient items to wear to get warm and to dissipate your perspiration. I have a lightweight option from Montbell and a bit heavier one from Thermowave I used to summit Island Peak.
Uniqlo DRY-EX T-shirt
The lightest and most breathable T-shirt I have ever tried, great for super hot and sweaty days. The only downside of being so thin that it is very prone to wear and tear.
Marmot Hiking T-shirt
A mid-weight synthetic hiking T-shirt which is cooler than merino but more resilient than the DRY-EX.
Montbell Chameese Fleece Jacket
A simple fleece jacket, light, warm, and has many useful pockets. O good option for flights as it has a zip to regulate temperature, but can get pretty warm, fits all your sleep gear and documents. A higher-end option could be a merino hoodie like this one from Icebreaker.
Montbell Alpine Light Down Jacket
Not cheap, but a great piece of kit with an unbeatable weight-to-warmth ratio. Packs very small and is warm enough for -10°C with suitable layering.
Montbell Superior Down Vest
The ultralight option to get some extra warmth but no bulk. Good when you are not sure if it will be cold or not, but definitely not cold enough for the down jacket.
BUFF Synthetic Neckwear
The most useful item by weight – can work as a neck warmer, thin hat, face mask to protect from dust, wind, or snow, eye mask for sleep. If you want to be extra specific, there are thicker merino ones for winter and super-thin synthetic ones for summer.
Julbo Shield REACTIV 2-4 Polarized Photochromic Sunglasses
If the trip includes hiking (especially on snow), deserts, or being on the water, these are great. They are photochromic between CAT 2-4, thus they work fine for normal wear but can get dark enough for a sunny day on the snow at 6000 m. The only negative is that their neck strap is useless, so I got one from Montbell. For urban trips, I would just take a random pair of Ray-Bans.
Marmot Minimalist rain jacket
A 2018 model with Goretex Paclite. Incredibly light and packs super small. Good for wind and light rain, but wets out during stronger rain. Thus for multi-day hiking I bought an Arcteryx Beta hardshell. But it seems the newer Marmot model have improved waterproofing.
Random Nike Cap
You will need a hat of some sort, simple baseball caps seem to work best in most scenarios. I used to own a pretty nice synthetic Salomon running cap, but that got lost in the sands of time.
Mountain Hardwear Scrambler 35L Roll-top Backpack
I can’t find the exact model of this pack online, but it is an old-ish very simple rock-climbing backpack with a roll-top closure made from tough waterproof material. Similar to Hyperlite Summit 30, but much cheaper as I bought it used. Roll-tops are great for optimizing storage-to-weight ratio, being tough, and with very few parts to break. The only two negatives are that they have no compartments and no quick access to the stuff in the bottom of your pack.
Sometimes one trip has a -5-40°C range like Ecuador or Ethiopia, and this pack can fit all the stuff I need even for such a trip, including a big camera. It fits the carry-on luggage requirements by volume, but if I have my camera and hiking boots might be a bit overweight, in case I am hassled for that I would just wear the camera on my shoulder and wear the boots.
Casual Clothes
If the trip has a significant urban segment, I would bring ‘civilian’ clothes, namely ultra-thin and stretchy Lee jeans and a super-thin Lee long sleeve button-up shirt