I overpack on the best of days. But, I swear, with baby in tow, it is ridiculous. In addition to clothes for Little Man, we also packed: stroller (in a cool wheeled bag that cost as much as most strollers cost and didn't actually do something that defied physics like make the stroller take up less space....but alas), car seat, a cooler of baby food, most of which needs to be refrigerated, usual diaper bag, extra diaper bag filled with our favorite Bum Genius Super Diapers, various toys and rattles including this super awesome vibrating teether, extra blankets, bag for dirty diapers, thermos with hot water for bottles, several bibs and spit clothes among other things.
It's hard to travel light. Mainly, I think it's hard because we make it hard. Since I don't breastfeed, we have a ton of eating crap for the baby. But other than the stroller, I'm not sure what we could have left at home.