Take stock of your health before departing. If you feel a cold or other illness coming on, do whatever you can to take preventative measures, such as bringing along appropriate medicine.
Be sure you bring enough warm clothing, even it if means overpacking a bit. Better to be saddled with a heavy-duty winter coat you don't end up needing than to be stuck in the snow wearing only a sweatshirt.
It's a cliché, but take in all the healthy liquids you can during your travels, especially those with Vitamin C. In addition to other pluses, this will help avoid dehydration, which can lead to fatigue and other ailments.
Keep your hands germ-free, which helps prevent the spread of contagious illnesses. In particular, be sure to wash up after using a public (or airplane) restroom or putting your hands in well-traversed places, such as an escalator banister. Disposable hand sanitizers are relatively affordable (especially away from the airport!) and a great way to combat germs.
Go the extra mile to have a healthy meal. One factor in getting sick on the road is eating foods that we aren't used to, or that are just plain unhealthy, out of convenience. Next time you need to chow down at the airport, for example, take a look around before settling on the fast food joint-more airport eateries than ever are trying to provide nutritious options to the typical junky fare.
If you're on a medication schedule and will be crossing time zones, figure out the effect of the time change on your medication-taking before leaving. Your head will be clearer and you won't have to figure the calculations out while sitting on a red-eye flight at 4 a.m.
Wear sturdy shoes that have some reliable tread to them, and if you're driving, make sure you have snow chains should you be in severely cold weather. Countless injuries take place every winter from pedestrians slipping on sidewalk ice patches or cars skidding out of control on icy and snowy roads.
