mileage & ambient temperature
 

Where I leave, the temperatures are fairly high (85-100 F). How can I get the best out of every drop of fuel with those temps?

Those temperatures are perfect! I get the best mileage in the heat of my Texas summer. The engine is closer to operating temperature, so there's less warmup needed. All the bearings and lubricants are lighter and freer-flowing. Tires roll better. The air is less dense, and the ECU puts in proportionally less fuel - basically detuning the engine a touch.

Just stay away from the AC if you can. Some ideas to help:
windows open
just run the vent fan
drink cold water
park under a tree for shade
crack the windows open when you park to vent the hot air (sunroof is even better if you have one)
use a shiny windshield shade
tint your windows
drive a white car ;)
wear cool clothes
"pulse and glide" the AC if you need it - run it for a bit, turn it off until it gets too warm, turn it back on for a bit. Keep the fan blowing to scavenge all the coolness in between.

Just a word about keeping the blower on during EOC coasting - If you are a sucker for hard EOC'ing, you would be driving your batteries low dangerously, and the electric blower ON all the time would help you get stranded in awkward places. Keep an eye on that battery voltage, if you are gonna keep that blower ON all the time. Otherwise it is very good to pull all the cold that the AC generates. (Same goes for loud music and headlamps)

I'd put it in the following order:
Headlamps
blower
music