Seconding extra hydration during the day. Between 20 and 30 minutes before you leave eat just a few calories, perhaps an apple and a few crackers or other food just to get you home. This way you have maybe 150-200 carbs to get home on and then eat a good meal. Cereal and small sandwiches is a fine diet if you don't like lots of fruits and veggies (like me) and just want to eat simply with no junk food. Lots better than going out to eat!! I commute 17 miles each way and make due with some toast and cereal in the morning, a small lunch, and (since I am a student with a meal plan) eat dinner at school, come home, then eat 200 carbs so I'm not hungry all night.
Sounds like the heat is also doing a number on you too!