Having come back recently from holiday travel (as, more than likely, you have too), and having seen some of the abominations out on public display in certain transit centers, I'm going to put this out there as a half-assed public service announcement: How Not to Look Totally Horrifying When You Travel.
Also having just completed a whirlwind road trip (twenty hours of driving over a fifty-five hour weekend window), I can safely say that if you're traveling via car, I have no good advice for you. I have found it impossible to get out of a car after driving for longer than two hours without looking completely wrecked. Something about my Honda Civic apparently mats my hair, greases my face, and removes all eyeliner.
A few guidelines that make my life better when I go anywhere via bus, train, or plane:
1) wear a huge scarfy thing. I don't care if it's August. Bring it, at least, because although it may be 90 degrees in Chicago when you depart, you will step onto the train to St. Louis and realize that the train is kept at 60 degrees for the duration of the ride, and you will curse yourself as you huddle, goose-fleshed in your tank top, against the window to try to absorb some exterior warmth.
The scarf is a blanket/ impromptu pillow/ drapey scarf to hide the drippy stains from your airport chicken wings/ ad hoc cover-up for when your flight gets canceled and you have to stay in an airport-adjacent hotel, but hey, they have a hot tub! Plus they pack up to almost zero space, so you really aren't out anything for bringing it.
2) keep lip balm in your pocket. You do not know hell until you know being trapped, lip-balm-less, without access to your carry-on as you sit on the bus and feel your lips cracking and bleeding.
3) wear a dress. Seriously. I am fond of dresses for many reasons (like the fact that they conceal the consumption of airport chicken wings), but I swear that dresses are the best for travel. You'll be sitting down for potentially hours on end, and you don't want a waistband digging into your stomach to add to the general discomfort of being crammed into coach. Plus, you'll look like you've made an effort, which will make people treat you with a tiny bit more respect, and if you get stuck in some horrific travel nightmare where trains or flights are missed and you have to say "I need to speak with your supervisor", you are far more likely to be taken seriously if you're not wearing flannel pajama pants with Mickey Mouse on them.
Comfort is key, obvs, but comfort is not limited to sweatsuits. Tall socks + knee-length cotton-blend skirt + sweater = as comfortable as a Juicy tracksuit, and 10,000x less likely to make you look like a jackass.
4) from personal experience over christmas: make sure the telescoping handle on your rolling suitcase actually telescopes and extends. If it doesn't, you will end up hunched over like Quasimodo, dragging a pathetically unhelpful roller bag behind you while trying not to let this posture dislodge your purse from your shoulder and also your will to live.