For the real hot situations (like Rawdon or other difficult situations) I drink until I sweat again. It's a crude rule of thumb, but I never had a heat stroke if I followed it.
I basically just remind myself to drink even though I don't feel I need it. By the time you're really thirsty in a Rawdon like environment, it's too late.
For food, jerky, small amount of candy, anything that delivers protein and sugar fast.