The pain of putting on a slinky silk dress, stepping into a car, and exiting with a mountain range of wrinkles up and down your look is real. Celebrities avoid this scenario by sprawling out in their limos and lying as flat as possible, or, if they really trust their driver not to make any sudden stops, by crouching in a half-stand for the duration of the ride (not recommended, for obvious safety reasons). If you're not working with an extra-large vehicle, tell your friends (or cabbie) "sorry, but I'm going to need all three of those back seats." And, if you're taking public transportation in a wrinkle-prone outfit, opt to stand. Another option: only travel to formal events via party bus.
Celebrities who manage to stand under white-hot red carpet lighting without sweating through their gowns aren't beautiful poreless aliens—they've just brought in reinforcements. Specifically, sweat protectors, which are small patches of absorbent fabric backed with adhesive. They're designed to stick to your outfit's armholes, which means they're not ideal for sleeveless styles, but if you're worried about sweat stains you can always wear them in transit to your destination and toss them when you leave the car.