I'm a pretty light traveller, but have three space-heavy hobbies: books, pipes, and digital gear. I've rethought my walking outfit to accommodate the hot weather.
Basic outfit will be roomy tactical pants, a hot-weather T-shirt, and a lightweight sun shirt above. Gear will be carried in the pants' cargo pockets, and also in an overbelt, a "half-vest".
Half-vests are hard to find on the Web. They're also called game bags, or shooting bags. The usual configuration is a large sure-close pocket hanging over each front pants pocket, and a large open "game bag" hanging off the back. I got a great one from LLBean a few years ago for about $30, but it doesn't seem to be in their catalog now... soft comfortable green nylon with a mesh backing so it doesn't weigh against the thighs. The bellowed front pockets are 8"x9"x2" with velcro closures; the back pocket is dual-entry black mesh, about 20" wide by 9" tall. The beautiful part is that shirt-tails completely hide this overbelt's pockets... by buttoning the shirt I can almost lock access to all pockets, for extra security. Holds more than a standard waist-pack, and it doesn't stick out into space... very discreet.
Cabelas.com has a few half-vests now, with slightly different design. I've been testing my LL Bean rig lately and it has been performing well -- Nokia Internet Tablet in one front pocket, keyboard in another, map case in one back entry and a first-aid kit in the other -- very comfortable. Still a lot of spare room, which always helps a pocket's flexibility. Hope it holds up on the road.
Passport? During travel I'll use a leather travel wallet, but for daywalks I'm using one of those soft "around the neck holders", but with the strap looped around my belt, running down my pants leg. Result is that it hangs at shin level, and can be accessed by rolling up the pants leg. No direct body contact, a concern in the heat. I've been trying passport systems for awhile, and I think this may be the one.
Liquids? Buy cold tea and juice on the street, la. In the outback I might need a container of my own, but in urban areas in Asia that's not a problem.
Pants, shirts and socks, I'm not yet sure on the weight -- it's hard to test hot-weather gear in San Francisco! My heaviest pants are a new "hot weather" series from 5.11 tactical gear... khaki EMT style, with large back pockets than can hold a stethoscope, or a guidebook. The nylon is fast-drying, but I hope it doesn't chafe above 90F. My second pants are a navy ripstop nylon set from Woolrich, which was comfortable in Taiwan, and which has two extra ankle pockets, as well as kneepad pockets. I'm also bringing an ultralight set of off-white nylon convertible pants, which can be streetwear, shorts, or even nightwear for over-airconditioned hotel rooms. I'm not sure which ones I'll wear most.
Shirts also have the same uncertainties. 5.11 has a great "hot weather" nylon shirt with big ol' concealed-carry breast pockets. But I've also got two much lighter nylon shirts, as well as two Filson Featherweight cotton shirts. I may toss one during the final packing, but I hope these function as lightweight jackets regardless of what weather there is.
A Filson Travel Vest will be used during travel, and particularly when returning to the cold of San Francisco, but in the past it has been too warm for walking Hong Kong. Will probably also bring a small Duluth travel bag for the computer, in case I need to give the half-vest a rest.
Socks? Dunno... got three very lightweight polypropylene liner socks, two coolmax cotton ankle socks, two cotton crews, and one (maybe two) lightweight wool outers. With the kind of walking I do I need double-socks, and this gives me a range of weights to mix together, and also lets me wear socks while sleeping if the hotel room's AC is too insistent.
Luggage is a Filson carry-on (checked in with my tools), and a Filson Medium Field Bag. Smaller than what most people travel with, and sometimes tight for me, but easy to maneuver. I'm packing an expandable nylon duffle in case I need more space on the trip back.
I've spent a lot of time agonizing about sunglasses... the sidewalk bicycle traffic in San Francisco has convinced me of the need for rear-view mirrors, but after lots of testing, they all sort of suck. Glasses with internal mirrored coatings are very convenient but come in few styles... tiny mirrors glued within the glasses are a pain to position and offer limited field-of-vision... I'm resigned to the metal Take-A-Look mirrors (as opposed to the plastic Third-Eye mirrors) which clamp onto the glasses' earpiece. Great field-of-view, but not the most convenient to store, and people stare if a pedestrian wears them. But they work, and they let me buy new sunglasses while I'm there, so that's that.
No regular toolkit... right now it's just a small Leatherman Micra, attached by a foot of paracord to a magnetic compass. Not sure if I'll pack a larger toolkit for the hotel. Instead of my usual first-aid & toiletry kit I'll be wearing a larger 6"x7" cordura wallet from Eagle, carrying chapstick, nailclip, toothbrush, nasal saline, Purell, aspirin, bandaids, etc. I'll be bringing a few pipes and tobacco, but it's more humid there, and so it won't be as much fun to smoke. Light.
A red supplex nylon ballcap (everybody likes someone in a happy red ballcap), a pair of comfortable slip-on walking shoes and a lightweight pair as a spare, and a cane of strong lightweight Cocus Wood into which I've sanded grips before bleaching blonde and sealing with a few coats of Tung Oil.
That, and a ruggedized Argus Bean camera, that's my gear. Goal is to walk, and walk, and walk, and not to have a bag force the weight on one section of my body. A new strategy on the pack this time, let's see how it works!