Always work with the natural texture of your hair, especially if the weather is humid. Hair styling products help tremendously but it is unlikely your hair will remain pin straight if you have naturally curly hair. Another point to consider is your hairstyle. You may want to consider an updo or a compromise with a half-up hairstyle so that less hair cascades onto your shoulders.
If you feel your forehead starting to sweat, please, we repeat please do not add more powder. Doing so will only make your makeup looked caked on and will be magnified by the camera. Instead, use blotting papers to soak up extra sweat and any oil on your skin. If you wear contacts, ensure that you have eye drops or extra contact solution in your survival kit. If your eyes tend to dry out quick, bring an extra pair. The hot weather will expedite the time that it takes for your contacts dry out.
Ensure that you or your makeup artist is using waterproof mascara and avoiding cream-based products such as cream blush. Use a moisturizing lipstick when possible and avoid matte lipsticks.
Depending on how many layers your dress has or how breathable the material that your dress is made from is, you may sweat more than you expect. Avoid applying moisturizer the day of your wedding (the night before is fine) and consider using an absorbent body powder. Estee Lauder makes a moisture absorbent body veil powder that wicks away moisture continuously throughout the day, does not stain delicate fabrics and has a pleasant fresh scent. If possible, have a few small hand towels so that you can soak them in cold water and place on your skin to cool down if things get really hot.
Wearing heels in hot and humid weather is a recipe for blisters. Use a baking soda based foot spray or dust body powder onto your toes. If your shoes aren’t breathable, consider using shoe petal insert for the balls of your feet to keep your foot from sliding, reducing friction.