Suggestions for what to look for in travel-specific clothing..
Clothes are always personal, but in general, try to focus on multi-use, quick-dry, light-weight and comfortable.
Durability is actually less important if you're traveling long-term and packing just a few sets; they will wear out and you will need to replace them as your socks get holes, your shirts get stains and your swim trunks get forgotten in the shower; which is why I'm a proponent of inexpensive, easily replaceable stuff wherever possible.
That being said, there are a few hard and fast rules to live by.. 1) don't skimp on shoes - you'll be wearing these a lot and they must be comfortable, and ideally multi-use.. 2) always go for quick-dry clothing if possible - drying is the biggest inconvenience when you're washing every day, and quick-dry clothing makes it so much easier.. 3) start flexible - utilize convertible hiking pants and shorts that triple as workout clothes, beach or lounge-wear.. 4) stay flexible - aside from (potentially) big-ticket items like shoes, pants and jackets, everything else should be inexpensive and easily replaceable.
Lastly, zippered pockets are a traveler's best friend, I look for multiple zippered-pockets whenever I'm upgrading or changing out clothes; hopefully you won't have to do this too often for your pants and jackets, so plan ahead if you're purchasing clothes prior to your trip.
Pants - I pack two pairs of quick-dry, convertible hiking pants, although you could easily get away with one. I'm generally wearing one pair while the other is drying, and they have the added benefit of working fine as swim trunks/lounge-wear. I went with Columbia brand (women's here) as they were comfortable, light-weight and had plenty of zippered pockets.
Shirts - I recommend sticking to a generic, inexpensive brand - so long as they are quick-drying. I purchased a 5-pack of Real Essentials Crew-Neck T-Shirts (women's here) and picked my favorite four colors; for $33 total, it's the easy button and they're perfectly comfortable for every day wear.
I also pack a single, long-sleeve, quick-drying shirt (hood optional) - even for hot climates - as you'll appreciate the option to add a layer on those randomly chilly nights (search here on Amazon).
Socks - Anything will do, socks are cheap, take up minimal space and should always be easily replaceable on the road.
Underwear - I'll again recommend any generic brand, but it's worth noting that I love and exclusively wear Exofficio (anti-bacterial, odor-resistant) boxer briefs (women's here).. I'm sure there are comparable and/or identical generic brands that cost less, but when you find something you love, you stick with it.
Swimsuits - Men's suits are, by nature, light-weight and quick-drying - on top of that, I recommend finding a brand that has multiple, zippered pockets and a style/fit that allows them to double as workout gear (I pack two pairs). You may want to consider whether or not your shorts have a mesh lining; comfort is king when you're wearing the same clothes every day, so keep that in mind and stick with what you like if you're traveling long-term.
Unfortunately, I can't speak to the options for women, but thankfully swimsuits don't take up too much space, so I'd imagine the additional item wouldn't cause much of an issue.
Optional Clothing
Jackets - Jackets take up a lot of space, and by sticking to warmer climates, you can (hopefully) ignore this all-together, but for those of you traveling to cooler climates or multiple destinations, you may want to opt for a light-weight, water-resistant, compressible puffer jacket (men's here, women's here).
A word to the wise.. use clear nail polish to seal up any nicks or scratches, it's cheap and easy and it will give your jacket some extra life when you inevitably snag it on a tree branch.
Ponchos - You can buy cheap, throw-away ponchos anywhere, but if you're looking to reduce waste and don't mind the additional space, opt for a fancy one that doubles as a park blanket; check out Agptek or SaphiRose, or search "reusable lightweight ponchos" on Amazon for options.
Thermal Underwear - Even in the warmest of climates, it gets cold sometimes, so I (sometimes) pack one set of thermal underwear just in case; this is completely optional, as you can easily purchase additional layers if you find yourself in a cold spell.
Note: If you're traveling to cooler climates, and only cooler climates, it's actually just as easy to keep your bag small; you'll be layering your clothes every day, so you should still only have to wash socks, underwear and an undershirt on a regular basis.
