We've been to St. John several times, but without our kids. I would bring your formula as the grocery store is decent, but very expensive. Like others already said...bring your powder stuff just in case. The water is fine on St John. We drank it and never had any issues, but you can always buy gallons of water from the grocery store. I would definitely bring your stroller!
As for things to do...St. John is really all about the beautiful beaches. We hiked and snorkeled a bit, but it was mostly a relaxing vacation. Are you staying at a resort or renting a villa? Renting a jeep? The restaurants in Cruz Bay are wonderful!
Enjoy your vacation! I am so jealous! It is my most favorite place on earth
ETA: I would bring food that your little one likes. Even when DH and I go there we pack a suitcase full of food items since it is so expensive.
~H~
Mom to 3 sweet kids
2003 ~ 2005 ~ 2009