Anything and I mean ANYTHING that's in the shade and/or AC is your friend. We're from a hot location and spent several years living in FL. When we went last year, late summer, we basically just prioritized taking it slow and being relaxed. When we got hot, we took a break with cold snacks, or a QS meal in the shade, or an indoor show or ride. We didn't have a touring plan, we didn't rush, we just meandered, took every opportunity to find shade or AC, drank lots of water from QS locations, and dressed for the heat.
Hats. Hats with wide brims are your friend. Who cares if it looks good, just wear it. Trust me, a wide brimmed hat looks better on you than heat stroke. ::smiles::