Here are a few ways to perk up without inhaling a gallon of coffee. First, try and expose yourself to the brightest light possible. Take a walk outside for a few minutes, or sit by a sunny window.
Temperature also makes a difference.
The cooler a room, the more alert you'll feel, so head towards a fan or open the window if you're fading. Some Japanese office complexes have taken to pumping the aroma of citrus or spearmint through their ventilation systems because these two scents have a proven ability to increase alertness. Turn on a radio. Also try stimulating your brain for a few minutes by playing a video game on your computer. Use your lunch hour differently.