Ihope you're breastfeeding. That will make the trip a million times easier!
Plenty of diapers, wipes, etc
Several changes of clothes
Receiving blankets. I love these. They were used as a sun shade, for warmth, changing pad, burp cloth, face wiper, to dry off someone wet, cover while nursing, etc. Bring plenty!
A baby sling to 'wear' baby on you. I've walked through all the MK wearing my baby and her nursing. No one knew, and I didn't have to waste time just sitting...although that's nice too.