Don't use the USPS, that's absolutely illegal. Ship via UPS (which is *probably* legal, albeit against company policy) and be prepared with a little white lie when they ask you what you're shipping. That's what I do, at least. Pack the **** out of the box so the bottles aren't loose.
"I'm kind of toasted. But I looked at my watch and it's only 6:30 so I can't stop drinking yet." - Yooper's Bob "Brown eye finally recovered after the abuse it endured in Ptown last weekend, but it took almost a full week." - Paulie "no, he just doesn't speak 'stupid'. i, however, am fluent...." - motobrewer "... I'll go both ways." - Melana
Sign up for a UPS account online, print your own labels, and bring to a UPS dropoff point. If they can't ask you, you can't lie.
Also, if you are shipping for competition, do not use styrofoam peanuts or packing tape to secure your bottles...the competition folks don't like that so much. Packing tape on the outside of the box is fine of course.