One of the biggest challenges for me is to find vegan options while traveling. When eating at new restaurants on the road, can you be assured that there are no dairy products in the meals or even meat products such as a chicken based broth, etc.? When your only option is a convenience store at a gas station in the middle of the countryside, what do you eat? The answer for me sometimes has been 'nothing'.
Many times, I'll just skip a meal until healthy options are available or until I find a supermarket to buy fruit and nuts and other healthy products. It makes it hard sometimes when traveling with other people who aren't vegan or vegetarian - you don't want to be a complete pain every meal. This article offers some good tips on how to prepare for a roadtrip and eat healthy which is useful for everyone regardless of what you usually eat!
http://www.sacbee.com/2011/11/21/4070122/the-frugal-traveler-thrifty-tips.html