Rule 1) Hydration wins championships. Your biggest summer challenge will be drinking enough water and avoiding fireants.
Rule 2) Two garments: an undershirt/t-shirt that wicks moisture. A cover garment - I basically only roll with the CCC Tropic Weight Vest. Pockets are lined with loop velcro. You can easily stick pouches in them for holding all kinds of accoutrement.
Rule 3) Pocket carry is awesome when you want to roll light.
Rule 4) Kydex can't be left in the car. Leather doesn't soften much in the heat BUT it's terrible at retaining moisture. Just don't leave kydex in the car.
Rule 4) Sunshades for the car windshield are a MUST. Never - ever - ever - under any circumstances - touch the bare metal of a seat belt that has been in the sun. Nor should you sit on leather/vinyl seats or park benches that have been in the sun for >10 min.
Rule 5) Hydration wins championships
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Stick your G-lock in your holster and rock on with a cover garment - shirt or vest is fine. Like I said I have a couple of those CCC "shoot me" vests I wear often - no one has shot me yet. I have run IWB and OWB 1911s under the vest. My preference is usually SME + STI + Spare mag in pocket.