Thanks for writing. Some of my favorite heat-tolerant, drought-resistant annuals include:
Angel's trumpet: http://www.bhg.com/gardening/plant-dictionary/annual/moonflower/
Blue salvia: http://www.bhg.com/gardening/plant-dictionary/annual/salvia/
Tropical milkweed: http://www.bhg.com/gardening/plant-dictionary/annual/blood-flower/
Also: Do you put mulch on the soil of your container? If not, that should help, too. It will keep the soil from drying out as fast and can help keep the soil temperature from getting too hot.
Thanks for writing. I hope this helps!
Senior Garden Editor, BHG.com
Better Homes and Gardens