Are you sure that you will want to carry the cooler around all day? What will you do with it when you go on rides, etc. Just a thought!
We buy bottled water for our room, and take one with us in the morning. We have some of the water bottle carriers, so we each "wear" our water. We do buy ice cold ones at the parks throughout the day, figuring this expense in, since in the Florida heat, we need ice cold!