What to wear — México
Clothing usually constitutes the bulk of travelers' luggage. Most of it is redundant and can be eliminated by packing the bare minimum of everyday clothes, say, three items each of pants, socks, underwear, dresses, skirts, and shirts. Moreover, only bring clothes that can be hand washed in the bathroom sink and will dry overnight, eliminating the hassle of sending clothes out to be cleaned or, heaven forbid, schlepping down to the laundromat.
In winter and fall overnight temperatures in the mountains and higher elevations can be downright cold, making a warm coat essential, even in the farthest southern states of Oaxaca and Chiapas. And spring and summer nights can still be cool, making a light sweater often necessary. What's also often necessary is a sweater on first-class or executive buses. More often than not, the A/C is blasting and way too cold, even when its scorching outside.
Other important items are a raincoat, preferably one that breathes, made out of Gore-Tex® or similar material that can double as a windbreaker; walking shoes or hiking boots; and a good pair of hiking socks. For going out at nights pack at least one nice outfit and pair of shoes to match, though just putting on a nice shirt or blouse is often enough. A sturdy pair of flip flops or waterproof sandals, like Tevas or Chacos, are a must for the beach or shower stalls of questionable cleanliness.
It's almost a right of passage for novice travelers to find out the hard way that they've overpacked. Lay out everything that you think you are going need. If an item, especially clothing, is not absolutely necessary, don't pack it. In the end, you'll be thankful that you did.
Lastly, Mexicans dress neatly and cleanly, especially when going out to restaurants, churches, festivals, and other special events. Except in beach towns, Méxican men and women never wear shorts, and swimsuits are only worn at the beach. When visiting religious or cultural sites, visitors should dress appropriately. In all, Mexicans are tolerant of the way foreigners dress. Still, out of respect for the culture of the place you're visiting, you should try and adhere to their norms as much as possible. You'll often find your efforts appreciated and reciprocated.
The blog www.travelite.org has some good tips on traveling light, as well as some useful travel product reviews. For tips on what to bring for camping and hiking, read the article "Outdoors — México."