We just go! Sure I worry and check online about nearest medical facilities, probably overpack, but we try to have a good time.
We went to Mexico for a wedding when DS was about 2 1/2. Had a great time. I DID have to pack some spagettios in my luggage just in case he didn't like some of the food we had. Otherwise, we packed everything medically related in our carry-ons -- little lunch bag cooler for refridgerated meds, another bag with medications, nebulizer. Vest fits in most overhead bins.
I did check with his doctor in terms of any vaccinations or medications he might need. DS needed one for Hep A, which is now apparently a standard vaccine for kids. Other suggestion was LOTS of suncreen.
Two years ago we spent a week in Florida.