Drink tea. Yep, you read that correctly: tea, not coffee. In a study of 95 people who kept logs for ten workdays, drinking caffeinated tea without milk or sugar provided the best perceived performance, according to research led by Janet Bryan, a psychologist at the University of South Australia in Adelaide. Drinking tea without sugar was linked to decreased fatigue (though that's not the case when sugar was added). The researchers cite evidence that tea is rich in flavonoids, compounds that enhance cerebral blood flow, which seem to improve both cognition and mood. 
Eat chocolate. You've probably heard this before, but it bears repeating: Eating small amounts of dark chocolate may boost physical endurance. Mice fed epicatechin, the main flavonoid in dark chocolate, twice daily for 15 days ran farther in a treadmill test than mice fed a placebo; their muscles were also more resistant to fatigue, tests showed. These results occurred whether or not the mice underwent additional exercise training. Epicatechin increases the number of energy-producing mitochondria in muscle cells, explains Francisco Villarreal, a professor of medicine at the University of California, San Diego School of Medicine, who collaborated on the research. A preliminary study in people found "very similar effects," he says, but there is a catch: The benefits very likely disappear if you eat too much of the compound, probably because the cell receptors involved become overloaded. "What's surprising is that you only need small doses of the compound to generate large effects, and our data suggests that more is not better," Villarreal says. The optimal daily dose is found in a five-gram piece of dark chocolate, which is the size of two regular postage stamps, he says.
Listen to an upbeat song. Anyone who's ever been midway through an exhausting workout only to get a sudden boost from a peppy song (say, Taylor Swift's "Shake It Off"?) can attest to this one: "Music is incredibly powerful," says Tracy Anderson, a celebrity trainer. "It blocks out all the other noise in your head—anything that would make you stop exercising." And it turns out the beat matters: Research from Brunel University London in England shows that the more closely a song's beats per minute matches your own heart rate, the more motivating it is.
Carry almonds.
When blood-sugar levels dip too low, willpower dips along with it (which is why that cookie is so irresistible a few hours after your chopped salad). When your energy starts to flag, Joy Bauer, the author of The Joy Fit Club: Cookbook, Diet Plan, and Inspiration (Wiley), suggests refueling with an apple and a handful of almonds, yogurt and a banana, or roasted edamame, "a perfect combination of high-quality carbohydrates, fiber, and protein that doesn't need to be refrigerated."
Work out.
We know, we know. But according to Thomas Plante, a professor of psychology at Santa Clara University in California, "exercise increases blood pressure and heart rate and activates the whole sympathetic nervous system." For those with no major cardiovascular problems, "this wakes you up and gives you a healthy boost." The most energizing workouts, according to Plante's research: solo outdoor activities, which expose you to energy-boosting sunlight and "aren't so draining, because you don't have to worry about keeping up conversation."
Take a cold shower.
We weren't very excited to learn that a cool shower is better than a warm one. But Mark Mahowald, a professor of neurology at the University of Minnesota Medical School, says that simply making your shower a few degrees cooler will increase alertness. And if you're daring, some neuroscientists theorize that taking a truly cold shower (68 degrees) could increase levels of beta-endorphins and produce a sense of well-being, says Orly Avitzur, a neurologist in Tarrytown, New York. Adding a peppermint body wash or shampoo to the mix puts even more spring in your step, says Rachel Herz, the author of The Scent of Desire (William Morrow). "Numerous studies have shown that people are stronger, faster, and more attentive after exposure to peppermint," according to Herz. One such study, at Wheeling Jesuit University, found that athletes exposed to the scent could do more push-ups.
Hydrate.
As soon as you get up in the morning, drink at least two cups of water. "We all wake up dehydrated," says Susan Kleiner, a dietitian and the author of The Good Mood Diet (Springboard Press). This is a problem, considering that every biochemical reaction—all of our thinking processes and our muscle contractions—depends upon us having enough water. And temperature matters: There's data that "drinking cool water, rather than ice-cold or warm water, empties most quickly from the stomach to enhance hydration," says Kleiner. As for those rumors about adding lemon? Sure, a citrusy scent might make you feel peppier in the morning, but other than that, it's not doing all that much. "Probably the biggest difference is that it adds a little flavor and may increase the amount that someone may drink, and it's far better than adding sugar or non-nutritive sweeteners," says Kleiner.
Keep your iron and protein levels up.
"Whenever someone says she's low in energy, I immediately wonder whether her diet is also low in iron and protein," says Lauren Slayton, the founder of Foodtrainers, a nutrition-counseling center in New York City. (Iron deficiencies can leave you fatigued, and the amino acids in protein help you feel alert.) Apples with peanut butter, oatmeal with walnuts, eggs, dairy-free bean soup, or a handful of edamame are good options. Pumpkin, sesame, and sunflower seeds are high in B vitamins and protein, so they act like little pellets of energy."