1. Find real food to eat, not fast food, not chain food, not junk food.
2. Wash your hands often and don’t touch your face (esp. eyes).
3. Do not use germ-killing lotions; they kill the good germs as well as the bad ones. You want those good ones!
4. Hotel room? Wash a glass you’re going to use that day yourself, after the staff has washed them. (Do not rely on the staff to have cleaned them well.)
5. Pay for Wifi; every time I’ve paid it’s worked MUCH better than free wifi. Why get frustrated with free wifi?!
6. Travel in business or first class if you can; more oxygen there (and less likely to get sick).
7. Drink a good amount of water.

If Mr. Pink’s theory is correct, you might reasonably expect that those who spend their woking lives in aircraft cabins might be the worst affected. – They’re not.The air filters in aircraft cabins are HEPA standard: You’re not at risk as a result of recirculated bugs and germs, but you are if you are sitting next to somebody with a cold – just as on a bus, metro etc.Antiseptic cream doesn’t (and can’t) cure or prevent the common cold: Moist nasal passages however, do help lots of good things to happen, which is why I ram vaseline up my schnoz when going on crew rest – stops tubes drying out while sleeping (or trying to). Oh, the glamour! 

Having dry sinuses allows airborne germs to lodge in  your nose. Having wet sinuses keeps things flushed out. But, equally important is “humidifying” your sinuses on planes because of the dry air.

Or maybe I’m missing something. boingboing wifi? I like it!

Mark, I thank you for posting this.  I will be using at least two of his tips during my upcoming business trip.

http://scuba.about.com/od/divemedicinesafety/p/Ear-Equalization-Why-And-How-Do-Divers-Equalize-The-Pressure-In-Their-Ears.htm 

Alas, my particular sense of entitlement dictates that I cannot assimilate your tip as you failed to supply it on SACD read by Hugo Weaving while Mr. T takes his first banjolele lesson in the background.

“I’ll show you how to set up a router to multiplay Terraria.  Got your pen and paper handy?”  ::bangs head against wall repeatedly:: 

Ok Mom, I’ll change my underwear and wear a jacket when it’s cold too…

Ask which line will be the quickest?  You get pointed to a line and you have to go there.  Try to finesse your way into a premier security line?  Sigh.  Resist putting on the TV the minute you walk in the hotel room  or else you’ll end up sitting there for hours.  Really…that’s a thing? Businessmen are the quickest through security lines?  Sometimes, yes, but they’re just as likely as to take longer, between having to pull out and turn on the laptop and forgetting things in their pockets so they have to go through 3 times before they’re clear.

And everything already said above about antibiotics, viruses vs. bacteria, and plain old petroleum jelly.

My tips:
#1: Have two sets of personal toiletry.  Your travel set and your home set. 
This way, there’s no risk of forgetting something.  The toiletry bag should have a crush-proof section – modify it if necessary. 
#1a: If you use an electric toothbrush that uses ‘AA’ batteries, flip one of them over into the wrong position, so that even if the power switch gets turned on, it won’t.

#2: Shower before you travel and wear a fresh set of clothes.  You’ll find that you’re less itchy and that you pick at yourself a lot less.

#3: Drink water.  Lots of it.  You GI tract will thank you.

On the other hand, I fully endorse trying international McDonalds.  Having beer and fries brought to your table at the Brenner Pass McD’s while looking out at snow covered Alps is awesome.

Still, for avoiding colds and infections, nothing works better than being a hermit.