Labor and birth is hard, physical work. Your uterus is a muscle -- the strongest muscle in the human body, in fact. With each contraction, your uterus contracts and releases (approximately 200-400 times or more throughout labor, depending on the length of labor). Add to that the force it takes to push out a baby (a whole lotta force!), and you're looking at a woman who is really working hard during labor and birth -- sometimes for more than 24 hours!
Like any other major, prolonged physical activity (sports game, running, hiking, swimming, biking, etc.), labor and birth require hydration and nutrition to maintain your stamina. And, similar to other physically demanding events, you may do better to seek food and drink that digests easily and is packed with nutrients and electrolytes. For example, laboring women don't usually crave a loaded slice of pizza and a giant Coke (though some do!). The following list of great labor foods are staples that laboring women often turn to, and provide the best bang for the buck, so to speak:
Water -- it's on the top of must-haves; sip it often throughout your labor to stay hydrated
Coconut water -- natural electrolytes!
Fruit juice or smoothies
Simple carbohydrates, like bread, muffins, crackers, and plain pasta
Hard candy -- not very nutritious, but can cure a dry mouth and curb nausea
Gel packs -- used by endurance athletes because they are easy to digest and process quickly for a boost of energy
You might be thinking, "But I've heard you can't eat during labor?" For many years, doctors have restricted laboring women from eating and drinking during labor (ice chips only!), but the evidence has emerged and it has found, in fact, that it is safe to drink and eat during labor and birth. To learn more, read a review of the research by Evidence Based Birth and a study on eating and drinking in labor from the Cochrane Summaries.